Today I formated my HD, installed Windows XP SP3, got latest drivers and now I'm installing WoW.
All this, because WoW has been starting to act up on me. If WoW would "stutter", like when entering some resource heavy place, there would be a good chance it would continue to "stutter" every 10 to 15 seconds no matter what. Even the character choosing screen "stuttered". Only way to get rid off it was to re-start WoW.
So since WotLK requires SP3 I got it, and since I had never formated my 4-5 year old computer I did that too. I really hope this helps, because I haven't got enough money for a new computer.