I was so disappointed at how my new PC with a Phenom 9950 , GTX 260 and 3.5 GB of RAM was running WotLK. Yesterday I was browsing HardOCP and saw thet NVIDIA released some new beta drivers that are primarily for GTA IV but they improved the framerate in WoW by a significant amount. I use Windows XP 32 bit but they have them for 64 bit XP and 32/64 bit Vista as well.
http://www.nzone.com/object/nzone_gtaiv_downloads.html