I'm hotkeying this next paragraph, because it seems everyone has the same misconception:

"64bit, Vista, 8gb ram and WoW: Don't bother, World of Warcraft is a 32 bit application and runs on a 32 bit emulator in Vist64 called Windows on Windows (Yes WoW-on-WoW) and is still limited to the same restrictions you are accustomed to. That said, ram is cheap, other games are 64bit compatible, hopefully Warcraft will be one day, but don't expect ANY performance increases due to using more than 4gb ram."

Specific to this case, expect lack of ram to be the bottleneck.