Not sure what you guys mean by hardcore, serious classes that need powerful computers. I know many of the fine arts guys and even the graphic design majors (I'm CGA which is the technical, programming side of art like photoshop plugins, web coding(flash, mysql, php, ect.), and visualization. I still take the fine arts classes though!) that get by fine on dated or even non-existent hardware and use the school's facilities for any of the larger work. It's not like you can just hook your ibook up to the RIP and print anyway. I say save the cash and keep what you have as it will be perfectly fine for anything you have to do and your school will provide the machines to do anything that it can't. besides, you will be surprised at how much you won't use it.
laptops blow for graphics work anyway. There, I said it. You will agree with me when you try to load a 1 gig psd before you go to class and it finishes when you get back. Forever. Make sure you have a good desktop (your's will do fine if your hard drive doesn't suck) and you are set. Files can be transferred all around campus on the network, so that isn't a problem.
also, note to prefrosh: No one really takes their laptops with them to class. It ends up being a huge distraction and the teachers generally hate it. A few guys do, but those are the guys who probably sleep with them too.
finally, remember these 2 things:
1. If you suck, get out now as the market is so saturated that you will not have a job. That is 100% truth. I have seen it with some actually good designers, so it's still iffy.
2. A better brush does not make you a better painter than Chagall. A better computer will not make you better than you are. Focus on your hand skills. If it can be done by computer or hand, do it by hand. Take the time and you will get much better than you would by taking the easy route.
Just some tips...
Good luck.