512 DDR 2
WXGA screen at native reso.
I found the game to play fine. The only time I experienced significant lag or drop in fps was entering IF. However, I think this is more of a RAM issue than anything. If you haven't noticed, once you enter an area you can instantly click on another Player and inspect their gear with no delay. I have been told that this is due to all that info being loaded to your PC so places like IF are big on RAM.
Overall, WoW is not too demanding on a PC. I also play on an old Alienware I bought back in October '03 that is a P4 2.53 with 768 RDRAM and a NVidia Ti 4600 128 without any trouble at all.
As a side note, Blizzard is getting ready to update their server hardware in the coming months so some performance improvements should be seen by everyone. However, I think this will mostly concentrate on Log-in queues but we shall see. Should be starting early April.