The retail XP qualifies.
Factory OEM does not qualify except on the same machine.
To repeat: you can SysPrep it and it will start up on the new hardware like a new install but with all of your customizations, requiring reactivation and possibly the Option Three workaround in Clean Install with a Upgrade Windows 7 Version
If you dont' like that result you can boot the Win7 installer to clean reinstall, it should see an OS to allow use of key during install. If not leave the Product Key blank and after install do the workaround to activate.