vBSEO is an SEO mod for vBulletin. Amongst many other things it it rewrites the URLs to make them more search engine friendly. If you compare the URLs on this site to a vanilla vB install as you navigate the forum, you will see the difference.
Th URL rewrites which is one of it's most useful features require Apache with mod_rewrite. Your site is running on a Microsoft server so if you're interested in it, you should have a word with
Phil at OpenMind to see if he can do anything about about rewriting the URLs. There are some mods for MS servers to do this, see
http://www.isapirewrite.com/ for example.
Even if you can't rewrite your URLs,
vBSEO is still a very useful mod for vB due to it's many other features such as the automatic pinging of services such as pingomatic when new threads are created and changing all your external links to use nofollow unless you put the URLs on your whitelist (This last one also has the advantage of making your site less attractive to some spammers due to you removing any search engine benefit they will gain by link spamming your site),
vB works very with search engines without any modifications but this mod does help and made a noticeable difference to this forum's search results.