Look at a Netbook.
We have a desktop, 17 inch screen and use it once in a blue moon.
We have a 15.4 laptop and use it instead of the desktop BUT
We have just bought an Advent 4211 netbook and it is brilliant. Weighs a couple of pounds. You can balance it properply on your knee. No CD drive but 3 USB ports and an MMC card port. You can also get them with integral mobile wireless.
For college use it is supremely portable. The standard batter has a life of about 80-90 minutes but you can get 6 and 9 cell versions with double or triple the life.
Do get your hands on a netbook, you'll love it.