Could you define what you mean by nulled version?  If vbulletin requires a license (which I believe it does) we would not allow any illegal work around or hacks that allows you to not pay for the script or software.

As Mitch said, LP will not permit you to use software hacked to get around licenses (if that's what you mean by "nulled"). That said, there are plenty of FREE  forums, blogs, content management systems, and others available for installation, including SMF, WordPress, Nucleus, b2evolution, Geeklog, Joomla, Mambo, phpWCMS, phpWebSite, Post-Nuke, and Siteframe. And that's just what's available under cPanel > Fantastico scripts -- you can install many other free ones on your own. You're not limited to VBulletin, if that's the only forum you've heard of.