Given your situation, you have your answer....or get a netbook (hack it of course) and build a nice i5 rig for $1500Aus.
Worst case, screw the netbook. You still have the laptop, and despite old, it's still good for typing notes (if your professors & classmates won't want to strangle you for it), checking email, and browsing. Enough to allow you to save additional funds for a netbook later at any rate.
Nice....Apple users have felt the lack of lubricant while visiting the Apple sales floor to buy their towers.