Index: wp-includes/class.wp-scripts.php
===================================================================
--- wp-includes/class.wp-scripts.php	(revision 21548)
+++ wp-includes/class.wp-scripts.php	(working copy)
@@ -96,7 +96,7 @@
 
 		$src = $this->registered[$handle]->src;
 
-		if ( $this->do_concat ) {
+		if ( $this->do_concat && ( !isset($this->registered[$handle]->extra['conditional']) || !$this->registered[$handle]->extra['conditional'] ) ) {
 			$srce = apply_filters( 'script_loader_src', $src, $handle );
 			if ( $this->in_default_dir($srce) ) {
 				$this->print_code .= $this->print_extra_script( $handle, false );
@@ -119,11 +119,45 @@
 
 		$src = esc_url( apply_filters( 'script_loader_src', $src, $handle ) );
 
-		if ( $this->do_concat )
+		if ( $this->do_concat && ( !isset( $this->registered[$handle]->extra['conditional'] ) || !$this->registered[$handle]->extra['conditional'] ) ) {
 			$this->print_html .= "<script type='text/javascript' src='$src'></script>\n";
-		else
-			echo "<script type='text/javascript' src='$src'></script>\n";
+		} else {
+			$start_cond = $end_cond = '';
 
+			if ( isset( $this->registered[$handle]->extra['conditional'] ) && $this->registered[$handle]->extra['conditional'] ) {
+				// By default, assume the conditional will target IE
+				$target_ie = true;
+
+				// If an array is passed in the conditional parameter, extract conditional and browser target
+				if ( is_array( $this->registered[$handle]->extra['conditional'] ) ) {
+					if ( isset( $this->registered[$handle]->extra['conditional']['condition'] ) ) {
+						$target_ie = isset( $this->registered[$handle]->extra['conditional']['target_ie'] ) ? (bool) $this->registered[$handle]->extra['conditional']['target_ie'] : true;
+
+						$this->registered[$handle]->extra['conditional'] = $this->registered[$handle]->extra['conditional']['condition'];
+					}
+					else {
+						$this->registered[$handle]->extra['conditional'] = '';
+					}
+				}
+
+				// Build the conditional, including the non-IE comment if necessary.
+				$start_cond = "<!--[if {$this->registered[$handle]->extra['conditional']}]>";
+
+				if ( ! $target_ie )
+					$start_cond .= '<!-->';
+
+				$start_cond .= "\n";
+
+				$end_cond = "<![endif]-->\n";
+
+				// Fail gracefully if the user doesn't pass the right data
+				if ( empty( $this->registered[$handle]->extra['conditional'] ) )
+					$start_cond = $end_cond = '';
+			}
+
+			echo "{$start_cond}<script type='text/javascript' src='$src'></script>\n{$end_cond}";
+		}
+
 		return true;
 	}