Desktop replacement help needed

I'm planning on buying a desktop replacement soon. I've been looking at Asus mainly with a budget ceiling of 1400-1500. Mainly, I need something reasonably fast and futureproofed (T7200ish, 2 gigs of ram) with a good videocard (I'd like a 7700, but an X1600 seems more likely). Gaming isn't my main priority (this is for school), but a gaming capable machine would be preferable. I'm not sure on whether I should get a 5400rpm 160 gig drive or a 7200rpm 100 gig drive; I've heard conflicting things about what's best for mobile use. The computer I've been considering most serious is an Asus Z96J from this site, as all the Dell machines I've seen have had rather unimpressive specs for the price, and I can't afford Apple markup. I looked at the Asus G1, but the price difference between it and the Z96J is over 400 with the only difference being the 7700 over the X1600 and the hideous omg1337 case over the bland-but-sane one. If there are alternatives, though, I'm definitely interested. Any advice would be welcome.

5400RPM vs 7200RPM is dependent on how you use it. If you don't mind losing the space and a little battery time, the 7200 will be noticably more responsive. So if you're going to be plugged in a lot and don't need 60GB more space, definitely the 7200.

I based that on a conversation I had yesterday with a friend (who works in desktop support) about a laptop that had a 5400RPM drive capable of being "underclocked" to 4200RPM to save battery life. I'll try and research this some more if I get the chance tomorow.