i have to agree with psylocke, i never understood the wisdom of getting bleeding edge hardware if you wont be using its potential anyway. with computers, if you want something for the future, then buy it in the future.
get the 3ghz core2duo since it takes a a while for applications (other than games) to catch up to hardware anyway. pero kahit sa games naman usually sa GPU ka maghahabol.
gawin mo 4Gb yung RAM mo, then get a couple of fast hard drives, put 'em on different cables and create pagefiles on each one.