C2D iMac 20" or 24" 😀
Faster processing, much larger and faster 7200 RPM storage, dedicated VRAM up to 256 MB and a big bad beautiful display for page layout or multi-tasking or movies.
Go for 2 GB RAM if you can.
My daughter and her roommate both have Apple notesbooks at college.
They leave them chained to the table with their security cable.