BTW, Windows Media Center Edition is essentially Windows XP Professional with a few multimedia add-ons. Give it a try before you fork over any more money to Microsoft.
Upgrade editions of XP are merely full versions that looks for current installs or install disks before permitting an installation. With XP upgrade editions, you don't need to install over top of another Windows. All you need is the install disk for a previous OS.
Vista is the exception. It requires you to have XP installed before it will upgrade it. It's not because it's all that different from a full version of Vista. It's just another attempt by Microsoft to prevent piracy. Just like their awful Genuine Advantage gunkware.
That said, I dislike upgrading an OS. If you have an upgrade version, have the previous OS disk handy and do a full wipe of your drive before installing. Clean installs tend to be more stable.
