Re: 600$ to burn!
There are a lot of choices available in your price range. You might want to consider some of the newer ultra-light portables such as the HP 2133 or the new Asus Eee PC.
Both can be purchased with either Linux or WinXP. The new Asus Eee 900 PC with Linux comes with a 20GB solid-state drive, a 8.9in screen, and weighs less than 2 pounds.
Have fun! Good luck at college.
Software expands to consume available system resources.
Be cautious, be vigilant, and beware of omnipresent Big Brother.