Hm...
In template
lsearch find:
HTML Code:
<script type="text/javascript" src="clientscript/vbulletin_ajax_live_search.js"></script>
<link rel="stylesheet" type="text/css" href="clientscript/vbulletin_css/live_search.css" />
Replace:
HTML Code:
<script type="text/javascript" src="forum/clientscript/vbulletin_ajax_live_search.js"></script>
<link rel="stylesheet" type="text/css" href="forum/clientscript/vbulletin_css/live_search.css" />
Just you use another path to forum.