Get a 512 MB Graphics Card. 320MB is not enough. Two 10K RPM drives should be enough.

Personally I suggest the following Hard Drive setup.

Whatever size you require for your OS - SATA2 7200 RPM. The key with your OS is the sustained data transfer rate. Which is why we go for a SATA2 Drive.

You then install WoW on some 10K RPM drives. I'd recommend 2x WoW installs per drive. With a seek time of 3.9 seconds, the Raptors are easily the best. SATA 1 though, so not advisable for file storage due to the slower data transfer rate.

Storage drive - SATA2 500GB or larger.