I could just do an upgrade from XP but would rather do a clean windows install.
You can't, actually. Windows 7 doesn't support in-place upgrade from XP, and it especially doesn't support an in-place upgrade from XP x64. Your only option is really to do a clean install, and use their Transfer utility to copy files over.
Also I'll warn you that their Transfer utility does not copy program files, only data and settings. If you want to keep your WoW folder from XP->7, you need to back it up to a separate hard drive or partition before installing.
With Vista, I didn't have to touch the WoW folder when I did the in-place upgrade to 7, it just worked seamlessly out of the box.