13. UPGRADES. To use upgrade software, you must first be licensed for the software that is eligible for the upgrade. Upon upgrade, this agreement takes the place of the agreement for the software you upgraded from. After you upgrade, you may no longer use the software you upgraded from.This means that you would not be able to dual-boot Windows XP (or whatever you upgraed from) or run it in a Virtual Machine. But this also means that if you do not like Vista you will be unable to revert back to Windows XP.