Index: wp-admin/includes/class-wp-theme-install-list-table.php
===================================================================
--- wp-admin/includes/class-wp-theme-install-list-table.php	(revision 19998)
+++ wp-admin/includes/class-wp-theme-install-list-table.php	(working copy)
@@ -162,12 +162,8 @@
 		$theme_names = array_keys( $themes );
 
 		foreach ( $theme_names as $theme_name ) {
-				$class = array( 'available-theme' );
-				?>
-				<div class="<?php echo join( ' ', $class ); ?>"><?php
-					if ( isset( $themes[$theme_name] ) )
-						display_theme( $themes[$theme_name] );
-				?></div>
-		<?php } // end foreach $theme_names
+			if ( isset( $themes[$theme_name] ) )
+				display_theme( $themes[$theme_name] );
+		} // end foreach $theme_names
 	}
 }
Index: wp-admin/includes/theme-install.php
===================================================================
--- wp-admin/includes/theme-install.php	(revision 19998)
+++ wp-admin/includes/theme-install.php	(working copy)
@@ -133,9 +133,17 @@
 	if ( empty($theme) )
 		return;
 
+	$class = array( 'available-theme' );
+
 	$name = wp_kses($theme->name, $themes_allowedtags);
 	$author = wp_kses($theme->author, $themes_allowedtags);
 	$desc = wp_kses($theme->description, $themes_allowedtags);
+	$screenshots = (array) $theme->screenshot_url;
+	$num_screenshots = count( $screenshots );
+
+	if ( $num_screenshots > 1 )
+		$class[] = 'has-screenshots';
+
 	//if ( strlen($desc) > 30 )
 	//	$desc = substr($desc, 0, 15) . '<span class="dots">...</span><span>' . substr($desc, -15) . '</span>';
 
@@ -151,10 +159,13 @@
 
 	$actions = implode ( ' | ', $actions );
 	?>
+<div class="<?php echo join( ' ', $class ); ?>">
 <a class='thickbox thickbox-preview screenshot'
 	href='<?php echo esc_url($preview_link); ?>'
 	title='<?php echo esc_attr(sprintf(__('Preview &#8220;%s&#8221;'), $name)); ?>'>
-<img src='<?php echo esc_url($theme->screenshot_url); ?>' width='150' />
+<?php if ( ! empty ( $screenshots ) && false !== $screenshots[0] ) : ?>
+<img src='<?php echo esc_url($screenshots[0]); ?>' alt='' data-num-images='<?php echo $num_screenshots; ?>' />
+<?php endif; ?>
 </a>
 <h3><?php
 	/* translators: 1: theme name, 2: author name */
@@ -183,6 +194,7 @@
 	<div class="star star1"><img src="<?php echo admin_url('images/star.png?v=20110615'); ?>" alt="<?php esc_attr_e('1 star') ?>" /></div>
 </div>
 </div>
+</div>
 <?php }
 	/*
 	 object(stdClass)[59]
Index: wp-admin/includes/class-wp-themes-list-table.php
===================================================================
--- wp-admin/includes/class-wp-themes-list-table.php	(revision 19998)
+++ wp-admin/includes/class-wp-themes-list-table.php	(working copy)
@@ -130,16 +130,15 @@
 
 	foreach ( $theme_names as $theme_name ) {
 		$class = array( 'available-theme' );
-	?>
-	<div class="<?php echo join( ' ', $class ); ?>">
-	<?php if ( !empty( $theme_name ) ) :
+
+	if ( !empty( $theme_name ) ) :
 	$template = $themes[$theme_name]['Template'];
 	$stylesheet = $themes[$theme_name]['Stylesheet'];
 	$title = $themes[$theme_name]['Title'];
 	$version = $themes[$theme_name]['Version'];
 	$description = $themes[$theme_name]['Description'];
 	$author = $themes[$theme_name]['Author'];
-	$screenshot = $themes[$theme_name]['Screenshot'];
+	$screenshots = (array) $themes[$theme_name]['Screenshot'];
 	$stylesheet_dir = $themes[$theme_name]['Stylesheet Dir'];
 	$template_dir = $themes[$theme_name]['Template Dir'];
 	$parent_theme = $themes[$theme_name]['Parent Theme'];
@@ -159,10 +158,16 @@
 	$actions = apply_filters( 'theme_action_links', $actions, $themes[$theme_name] );
 
 	$actions = implode ( ' | ', $actions );
+
+	$num_screenshots = count( $screenshots );
+
+	if ( $num_screenshots > 1 )
+		$class[] = 'has-screenshots';
 ?>
+	<div class="<?php echo join( ' ', $class ); ?>">
 		<a href="<?php echo $preview_link; ?>" class="<?php echo $thickbox_class; ?> screenshot">
-<?php if ( $screenshot ) : ?>
-			<img src="<?php echo $theme_root_uri . '/' . $stylesheet . '/' . $screenshot; ?>" alt="" />
+<?php if ( ! empty ( $screenshots ) && false !== $screenshots[0] ) : ?>
+			<img src="<?php echo $theme_root_uri . '/' . $stylesheet . '/' . $screenshots[0]; ?>" alt="" data-num-images="<?php echo $num_screenshots; ?>" />
 <?php endif; ?>
 		</a>
 <h3><?php
@@ -182,8 +187,8 @@
 <?php if ( $tags ) : ?>
 <p><?php _e( 'Tags:' ); ?> <?php echo join( ', ', $tags ); ?></p>
 <?php endif; ?>
+</div>
 <?php endif; // end if not empty theme_name ?>
-</div>
 	<?php theme_update_available( $themes[$theme_name] ); ?>
 	</div>
 <?php } // end foreach $theme_names
Index: wp-admin/js/theme-preview.dev.js
===================================================================
--- wp-admin/js/theme-preview.dev.js	(revision 19998)
+++ wp-admin/js/theme-preview.dev.js	(working copy)
@@ -54,10 +54,97 @@
 		return false;
 	} );
 
-	// Theme details
-	$('#availablethemes').on('click', 'a.theme-detail', function (event) {
-		$(this).siblings('.themedetaildiv').toggle();
+
+	// Toggle Theme Details
+	var currentTheme;
+	$('#availablethemes').on( 'click', 'a.theme-detail', function() {
+
+		var $this = $(this);
+		
+		if ( currentTheme !== undefined ) {
+			// remove active class/extended details div
+			$('.extended-details').remove();
+			currentTheme.removeClass( 'active' );
+			currentTheme.height( 'auto' );
+
+			// bail if the link clicked was the same as previously
+			if ( currentTheme[0] ===  $this.closest( 'div.available-theme' )[0] ) {
+				currentTheme = undefined;
+				return false;
+			}
+		}
+
+		// reset nextLower - has scope for now to possibly use for window resize reflow
+		var nextLower = undefined,
+			maxMargin = 50, // Max Margin allowed between theme and details div
+			detailsDiv = $('<div class="extended-details"><div class="themedetaildiv"><h4>Theme Details</h4></div><div class="screenshots"></div></div>');
+			
+		currentTheme = $this.closest( 'div.available-theme' );
+		var currentPosition = currentTheme.position().top;
+		var currentBottom = currentPosition + currentTheme.height();
+
+		currentTheme.addClass( 'active' );
+
+		// find the next div.available-theme that has a lower position().top
+		currentTheme.nextAll('div.available-theme').each( function() {
+			var $this = $(this);
+			if( currentPosition < $this.position().top ) {
+				nextLower = $this;
+				return false;
+			}
+		});
+
+		// insert the details div
+		if ( nextLower !== undefined ) {
+			nextLower.before( detailsDiv );
+		} else {
+			$('#availablethemes').append( detailsDiv );
+		}
+		
+		// now that it's generated, grab top of details div
+		var detailsTop = detailsDiv.position().top;
+		var margin = detailsTop - currentBottom;
+
+		/**
+		 * If the margin between the bottom of the current theme and details div
+		 * is greater than maxMargin, extend current theme to avoid whitespace.
+		 */
+		if ( margin > maxMargin)
+			currentTheme.height( currentTheme.height() + ( margin - maxMargin ) );
+
+		var themeDetails = $this.siblings( '.themedetaildiv' ).html();
+		$('.extended-details .themedetaildiv').append(themeDetails);
+
+		// do more screenshots
+		var screenshot = $('.screenshot img', currentTheme);
+		var src = screenshot.attr( 'src' );
+
+		if ( src !== undefined ) {
+			var numScreenshots = screenshot.attr( 'data-num-images' ),
+				screenshots = $('.extended-details .screenshots');
+
+			screenshots.append( '<div class="screenshot"><img src="' + src + '" /></div>' );
+
+			if ( numScreenshots !== undefined && numScreenshots > 1 ) {
+				var base = src.replace( /screenshot\.(jpg|png)$/, '' );
+
+				for ( var i = 2; i <= numScreenshots; i++ ) {
+					screenshots.append( '<div class="screenshot"><img src="' + base + 'screenshot-' + String(i) + '.png" /></div>' );
+				}
+			}
+		}
+
 		return false;
 	});
 
+	// if we resize, and there's a details div open, close it.
+	$(window).resize( function() { 
+		if ( currentTheme !== undefined ) {
+			$('.extended-details').remove();
+			currentTheme.removeClass( 'active' );
+			currentTheme.height( 'auto' );
+			currentTheme = undefined;
+		}
+	});
+	
 });
Index: wp-admin/css/wp-admin.dev.css
===================================================================
--- wp-admin/css/wp-admin.dev.css	(revision 19998)
+++ wp-admin/css/wp-admin.dev.css	(working copy)
@@ -4478,16 +4478,25 @@
 .available-theme {
 	display: inline-block;
 	margin-bottom: 10px;
-	margin-right: 25px;
+	margin-right: 10px;
 	overflow: hidden;
 	padding: 20px;
 	vertical-align: top;
-	width: 240px;
+	width: 300px;
+	border-top-left-radius: 3px;
+	border-top-right-radius: 3px;
+	-webkit-border-top-left-radius: 3px;
+	-webkit-border-top-right-radius: 3px;
 }
 
+.js .available-theme.has-screenshots {
+	background: transparent url(../images/stack.png) no-repeat 26px 5px;
+}
+
 .available-theme a.screenshot {
-	width: 240px;
-	height: 180px;
+	width: 300px;
+	height: 225px;
+	margin: 0 auto;
 	display: block;
 	border-width: 1px;
 	border-style: solid;
@@ -4496,13 +4505,66 @@
 }
 
 .available-theme img {
-	width: 240px;
+	width: 300px;
 }
 
 .available-theme h3 {
 	margin: 15px 0 5px;
 }
 
+.available-theme.active,
+.available-theme.has-screenshots.active {
+	background: #efefef;
+}
+
+.extended-details {
+	overflow: hidden;
+	position: relative;
+	margin-top: -13px;
+	margin-bottom: 20px;
+	padding: 5px 20px;
+	padding-left: 330px;
+	background-color: #efefef;
+	border-radius: 3px;
+	-webkit-border-radius: 3px;
+}
+
+#availablethemes .extended-details h4 {
+	margin: 1em 0;
+}
+
+.extended-details .themedetaildiv {
+	position: relative;
+	float: left;
+	width: 280px;
+	right: 310px;
+	margin-right: -100%;
+	margin-bottom: 20px;
+}
+
+.extended-details .screenshots {
+	position: relative;
+	float: left;
+	margin-top: 15px;
+	width: 100%;
+}
+
+.extended-details div.screenshot {
+	overflow: hidden;
+	float: left;
+	margin-right: 20px;
+	margin-bottom: 20px;
+	width: 300px;
+	height: 225px;
+	border: 1px solid #ddd;
+}
+
+.extended-details div.screenshot img {
+	display: block;
+	margin: 0 auto;
+	width: 100%;
+}
+
 #current-theme {
 	margin: 1em 0 1.5em;
 }
@@ -7423,8 +7485,7 @@
 }
 
 
-#theme-information .available-theme,
-.available-theme {
+#theme-information .available-theme {
 	padding: 20px 15px;
 }