What's the best tool to use to see how and if my forum i have on a site will be liked and spidered by google, and how deep it will go etc? Thanks!
I don't think there is such a tool ever made. If you turn on mod_rewrite then all major SEs will crawl it quite happily because they hate lengthy and parameters-rich URLs.
You don't need to do anything special to make vBulletin spiderable. It's perfectly spiderable right out of the box. Like any site you want to get spidered, all you need is links from other sites. vBulletin 3.5.x is even better than 3.0.x because it uses nofollow in appropriate places to prevent duplicate content or pages that require the user be logged in (for example links to send someone a PM).