Index: category-template.php
===================================================================
--- category-template.php	(revision 20071)
+++ category-template.php	(working copy)
@@ -307,7 +307,8 @@
 		'name' => 'cat', 'id' => '',
 		'class' => 'postform', 'depth' => 0,
 		'tab_index' => 0, 'taxonomy' => 'category',
-		'hide_if_empty' => false
+		'hide_if_empty' => false,
+		'multiselect' => false
 	);
 
 	$defaults['selected'] = ( is_category() ) ? get_query_var( 'cat' ) : 0;
@@ -336,7 +337,7 @@
 	$id = $id ? esc_attr( $id ) : $name;
 
 	if ( ! $r['hide_if_empty'] || ! empty($categories) )
-		$output = "<select name='$name' id='$id' class='$class' $tab_index_attribute>\n";
+		$output = "<select name='$name' id='$id'".(($multiselect) ? "multiple='multiple'" : "")." class='$class' $tab_index_attribute>\n";
 	else
 		$output = '';