I really don't know how to answer you. Maybe I don't understand what you are trying to do. I thought you just wanted to turn on the rss feed for your vbulletin boards so you could import the feed into your wordpress site. If so, you just turn it on and then the feed url is
www.yoursite.com/external.php?type=rss2 and you would use that feed however you want on your wordpress site. You may want to read about this in the manual -
External Data Provider