If you'll be locking your bike outside on campus....then get a cheapish used bike that works well and fits you ok, the uglier the better, and get HEAVY DUTY locks (a heavy U-lock AND a heavy cable if possible). Campuses are major hotspots for bike thieves. Any new bike worth $300 or more is going to be an automatic target for thieves.
Once you are not on campus anymore you can start getting more beautiful/desirable bikes.
http://www.treehugger.com/files/2008...-bike-tips.php
http://www.cyclelicio.us/2005/09/lock-your-bike.html

Good luck and enjoy whatever bike you wind up getting!