VBulleting has 3 sites... not sure why but here they are...
This one :
www.vbulletintemplates.com - for all things to do with modifying templates only. You won't find anything about altering any of the php files or your database here. This is, essentially, a "how to" appearance-modification-only site, dealing with html templates and styles.
www.vbulletin.org -- this is where the bulk of major modifications can be found. This site deals with altering php files, your database and major additions to the vbulletin package. However, installing "hacks" may mean it will be difficult to get support at the next site...
www.vbulletin.com - the main product site where you should go if you experience any problems with the standard installation or if you're just having trouble finding your way around.