Despite claims that you need a pretty high-end PC to run Vista well, J2s site came up with a system that runs Vista with Aero Glass enabled for only $538 (not counting the price of Vista itself).

From looking at the parts list, he uses some pretty decent—but not spectacular parts—and actually manages to get 2GB of RAM in there. It's not going to win any speed races, but this thing costs less than a PS3.

How to Build an inexpensive Vista PC (Aero Enabled) [JJMelo]