Yep. 8 gigs of RAM is pretty useless.
My home comp has 4GB of DDR2 RAM and runs vista64bit...I rarely see it use more than 2GB of RAM when gaming + virus scans + firefox tabs in the background.
My main rig with 6GB of DDR3 RAM use no more than 3GB of RAM when I multitask and game like crazy.
I'd say get a good quad core (from your budget, I'd say get a AMD PhenomII quad, since they have the best CPUs for the price under $200) and 4GB of DDR2 or DDR3 double channel, or 6GB of DDR3 triple channel RAM will do just fine.