Blogs are sold over on vb.com (or they were, not sure if they sell them any longer). They now are included with the vbulletin suite (not out yet). You may code other pages and add them to your site, see these two articles on how to do that -
How to create your own vBulletin-powered page! (uses vB templates) or
[How-To] vBulletin API Basics: Creating Custom Pages & Misc.. You can try a search here and see if there is already a mod done to do what you want.