i never have understood the need for vbulletin. It is one of the few messageboards that dictates a liscence be bought. i guess it is a guarantee that support will be there over the years but there have been many free boards that are as robust or even better.
i have never tried a drupal messageboard but if it is the expense of the vbulletin that is at issue too , theres got to be one similar to drupal as a standalone from these
http://www.hotscripts.com/PHP/Script...rds/index.html