you can run Joomla (CMS) with vBulletin, there is a bridge script which will port your members from the vBulletin onto the Joomla (and the reverse) the bridge is called "VBulletin Duo Sync Bridge".
only thing i couldn't do with it yet, was pull vB threads onto it. however you can make article posts -- than inside link it back to the thread on the community.
another alternative for you. you can get joomla here
www.joomla.org