This is a good time to get a laptop. I see prices dropping all the time.
I picked up a small Acer 5315 for $350 at Wal-mart. It's not that light though. It also came with only 1Gig of RAM which I immediately upgraded to 2Gig as it is running Vista.
I see Compaqs and HPs going for $400-500.
Ebay will also get you a good deal but you need to be careful with whom you deal. I picked up an old Dell Inspiron laptop for $150 a couple of years ago, so those prices should also be down.
If you are traveling, try to get as light a unit as possible. HPs and Acer Travelmates are both fairly light along with many others.
Good luck choosing.