I kinda like the PM setup over on Yotatech who use vBulletin. You get a pop-up that tells you that you have a new PM.
You can also import the DB from UBB to vBulletin.
What I would reccomend if you do take on a move to something new, is setup the new forum in a different folder i.e.
www.xterraownersclub.com/forums/ then while the changover is happening you can test the new Forum along side the old one - until you are happy with the setup etc. Then just do a redirect on /forums.html over to /forum/ to do the final change over.
