If you consider a laptop, for your needs even a low end one will do just fine. At that price-point ($400 - $500 max) you're not that much more than NetBook cost, even cheaper than some NetBooks, so no reason I can come up with to consider a NetBook (unless you want their very small size). You will also get more bang for your buck with more memory rather than a more powerful CPU. If you want more speed for your buck, load a lightweight Linux on it rather than Windows. If you want blazing speed, boot Linux so it loads totally into memory, thus using your harddisk for permanent storage only (not for running the OS from). For me, one of the biggest decision points in buying an inexpensive laptop is the keyboard. There are some really terrible ones out there. And the very best are only mediocre compared to a desktop separate keyboard. Forget the trackpad - they are all horrid, and for emergencies only IMHO. Get an external mouse and don't worry yourself looking for a decent trackpad (there is no such thing).

If you're tempted by laptops, I'd say: (1) Inexpensive low-end model, (2) External monitor, (3) External Keyboard, and (4) External mouse. The money you save on buying the low-end model will cover the expense for the external components.