Thanks for the responses everyone - I'm quite convinced it's just heat as my card is nothing special being a 9600GT. This is something that probably wouldn't happen if I do get my super-rig with 2x 280GTX's and if it does i can always invest in some cooling measures.

Re the never reinstalling wow comment - I'm in the same boat as you, I don't think I've reinstalled the game for about 2 or 3 years.. I'll give it a shot deleting the files you mentioned - cheers.

Edit: to Nitro - I have 4gb ram (albeit cheap..) so I doubt that's a problem !