[Dave]

Well you're basically asking "someone go make me those htaccess rules". It's a pain to make such .htaccess rules.

Anyways beside that it's not possible to make both domain.com/forum-name and domain.com/username because there's no way for the server or vBulletin to distinguish when a forum name or username is used in the URL... unless you create some hooks that take care of that problem.

A more realistic and better approach would be:
domain.com/forum/forum-name
domain.com/thread/thread-name
domain.com/user/username

I can't help you out with it though.