Index: wp-includes/class.wp-scripts.php
===================================================================
--- wp-includes/class.wp-scripts.php	(revision 17167)
+++ wp-includes/class.wp-scripts.php	(working copy)
@@ -82,6 +82,8 @@
 		if ( !parent::do_item($handle) )
 			return false;
 
+		$start_cond = $end_cond = '';
+
 		if ( 0 === $group && $this->groups[$handle] > 0 ) {
 			$this->in_footer[] = $handle;
 			return false;
@@ -112,6 +114,11 @@
 				$this->ext_version .= "$handle$ver";
 			}
 		}
+		
+		if ( isset($this->registered[$handle]->extra['conditional']) && $this->registered[$handle]->extra['conditional'] ) {
+			$start_cond = "<!--[if {$this->registered[$handle]->extra['conditional']}]>\n";
+			$end_cond = "<![endif]-->\n";
+		}
 
 		$this->print_scripts_l10n( $handle );
 		if ( !preg_match('|^https?://|', $src) && ! ( $this->content_url && 0 === strpos($src, $this->content_url) ) ) {
@@ -125,7 +132,7 @@
 		if ( $this->do_concat )
 			$this->print_html .= "<script type='text/javascript' src='$src'></script>\n";
 		else
-			echo "<script type='text/javascript' src='$src'></script>\n";
+			echo "{$start_cond}<script type='text/javascript' src='$src'></script>\n{$end_cond}";
 
 		return true;
 	}