Just FYI, the upgrade versions are the same as the full version in every way except that you must have a previous, legitimate copy of Windows on disc with the upgrade version. For instance, you can do a clean install with the upgrade version, but you need a copy of Windows 98 or something in disc form that it can verify during the installation. Likewise, you can do an upgrade with the full version.
Put another way, buy the upgrade if you still have your Windows 2000 disc and you want the money savings or buy the full version if you don't have the 2000 disc or don't want the hassle of always having to keep the 2000 disc around just in case. The full retail license for XP allows much more than the OEM license. For instance, the OEM version can only be put on one machine ever. Stay away from that unless you'll not be getting a new computer or significantly upgrading your current computer anytime soon.
But yeah, aren't you in school? I can get a copy of XP from school for like $10. It's OEM, but... it's $10.