AMD might be a bit cheaper, but Intel is still probably a better choice. If you need something that you can use in class all day, then a netbook with an Intel Atom processor might be a good choice.
A netbook is just a mini-laptop...it does not have the performance, the big screen, the bluray/dvd drive, or any of that...but most of them have a battery life of 4 hours or more, and they are nice and small...and they cost a lot less (you can get them even cheaper and with built-in 3G internet from several wireless providors). If you are keeping your desktop, and just using the laptop for class, the netbook can be a very appealing option. Of course, if you are only going to have one computer, then you should probably avoid netbooks.