Index: wp-admin/js/theme-preview.dev.js
===================================================================
--- wp-admin/js/theme-preview.dev.js	(revision 19976)
+++ wp-admin/js/theme-preview.dev.js	(working copy)
@@ -54,10 +54,66 @@
 		return false;
 	} );
 
+
 	// Theme details
+
+	var currentTheme, nextLower;
+
 	$('#availablethemes').on('click', 'a.theme-detail', function (event) {
-		$(this).siblings('.themedetaildiv').toggle();
+
+		if ( currentTheme !== undefined ) {
+			// remove active class/extended details div
+			$('.extended-details').remove();
+			currentTheme.removeClass( 'active' );
+
+			// 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 to use for window resize reflow
+		nextLower = undefined;
+
+		var detailsDiv = $('<div class="extended-details"><div class="themedetaildiv"><h4>Theme Details</h4></div><div class="screenshots"></div></div>');
+
+		// get parent div.available-theme
+		currentTheme = $(this).closest( 'div.available-theme' );
+
+		// set active class for parent
+		currentTheme.addClass( 'active' );
+
+		// get top position of parent
+		var currentPosition = currentTheme.position().top;
+
+		// find the next div.available-theme that has a lower position().top
+		currentTheme.nextAll('div.available-theme').each( function(index) {
+			if(currentPosition != $(this).position().top) {
+				nextLower = $(this);
+				return false;
+			}
+		});
+
+		// insert/move the theme details div before that parent if found
+		if ( nextLower !== undefined ) {
+			nextLower.before(detailsDiv);
+		}
+		// if not found, insert before the end of the overall div
+		else {
+			$('#availablethemes').append(detailsDiv);
+		}
+
+		// set inner HTML of theme details div to the contents of $(this).siblings('.themedetaildiv')
+		var themeDetails = $(this).siblings('.themedetaildiv').html();
+		$('.extended-details .themedetaildiv').append(themeDetails);
+
+		// plus the HTML for the extra screenshots, to be pulled from... ?
+
 		return false;
 	});
 
+	// deal with window resizing and reflow, but only if there is something active
+	// $(window).resize( function() { } );
+
 });
Index: wp-admin/css/wp-admin.dev.css
===================================================================
--- wp-admin/css/wp-admin.dev.css	(revision 19976)
+++ wp-admin/css/wp-admin.dev.css	(working copy)
@@ -4441,16 +4441,25 @@
 .available-theme {
 	display: inline-block;
 	margin-bottom: 10px;
-	margin-right: 25px;
-	overflow: hidden;
+	margin-right: 10px;
+	overflow: visible;
 	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;
@@ -4459,13 +4468,58 @@
 }
 
 .available-theme img {
-	width: 240px;
+	width: 300px;
 }
 
 .available-theme h3 {
 	margin: 15px 0 5px;
 }
 
+.available-theme.active {
+	background: #f5f5f5;
+}
+
+.extended-details {
+	overflow: hidden;
+	position: relative;
+	margin-top: -10px;
+	margin-bottom: 20px;
+	padding: 5px 20px;
+	padding-left: 330px;
+	background-color: #f5f5f5;
+	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 .screenshots img {
+	float: left;
+	margin-right: 20px;
+	margin-bottom: 20px;
+	width: 300px;
+	height: 225px;
+	border: 1px solid #ddd;
+}
+
 #current-theme {
 	margin: 1em 0 1.5em;
 }
@@ -7386,8 +7440,7 @@
 }
 
 
-#theme-information .available-theme,
-.available-theme {
+#theme-information .available-theme {
 	padding: 20px 15px;
 }