Getting a new graphics wont help much.

Next best improvement yeh can do is disabling aero after that is start disabling other thing yeh don't need.

If yeh have multiple installations of wow yeh wont see an improvement in cities if yeh move em off to separate hard drives
only in zoning into an instance.

vista32 and xp can only use 4 gigs of memory

vista needs 2 gigs where as xp only 1 gig ( without paging anything out to the hard drive).