Get an Asus Eee 901. The reason I say that is it sounds like you want portability above all else. The 901 has the Atom CPU and it only weighs in at 2 pounds and costs about $400-$500.
It also has a SSD hard drive (20 GB) making speed to the HD (The laptops slowest component) lightning fast and not prone to crashing. I suggest buying a Linux version and loading your own XP to save $$$.
Without any more info, that is what i would steer you towards.
http://eeepc.asus.com/global/901.htm
-S
PS. Did I mention over 8 hours battery life?
PPS. Did I mention tiny too? I'm buying one for myself. Great to have something like this on an airplane or while traveling.
PPPS. 40 GB is more than you probably need if you don't plan to game.