MBP Severe Problems

Currently I am experience severe problems with my MBP. While playing WoW for about a half hour in one zone, then switching to a new zone my FPS drops down to 1-15 from around 40-55. This problem persists with the game until I relaunch, sometimes until I reboot. Seemingly unrelated to the first problem, recently I've had it where the entire UI is barely responsive for almost everything, opening/closing windows, switching applications, and opening/closing menus all require 20-40 seconds to happen. This problem becomes progressively worse until I have to force shutdown my computer (hold power button), force restart (cmd-ctrl-power button) is ineffective.

My main problem is the rarity of these issues, they can't be reproduced at will. I sent in my computer once before and it came back only listing Class I repairs, no parts were listed as being replaced. The problems persisted and continued to get worse. Does anyone have any suggestions on how I should handle this?

 

It's a 2.4 GHz Santa Rosa MBP from about 8 months ago with the 256 MB 5600M GT video card running Leopard. I have all the updates installed except for the most recent keyboard firmware and airport ones.

I'll try an archive-install of Leopard on monday, I just assumed I had a hardware problem it seems and never thought about it being the OS.