A suggestion:
This is a 530 dollar (500 dollars after rebate) Compaq. Looks like it is one of the better performing laptops in its price range. Decent screen resolution, processor (dual core), and RAM. Good hard drive size. 2 hour battery life. 3 USB ports and a memory card reader. Comes with Windows Vista.
However, it is a little on the big side – 6.6 lbs with a 15.6 inch screen. If your main concern is portability, you might want to sacrifice performance and quality for smaller size.