As an addendum to my previous post, again, this is all a guess based on your symptoms. It really would help if you were to cut and paste the output of the commands listed in my first post to confirm or rule out my suspicions. Also, I've tried to dumb it down a bit, but a more complete explanation of VMM on OS/X can be found here:
http://developer.apple.com/library/m...outMemory.html