ergophobe - 10:43 pm on Aug 30, 2011 (gmt 0)
For general tags (site wide): https://www.vbulletin.com/docs/html/main/vboptions_group_general
vbSEO does dynamic meta tags based on content for vb 3, but not for vb 4.
There are some meta tag plugins too, but not sure which versions they work with (but the Advanced Meta Tags plugin definitely includes 4).
Hope that helps