I'm trying to go from a trial copy of windows 7 enterprise to windows 7 ultimate for system builders. A website called addictive tips has a windows downgrader which seems to work well with retail versions of windows 7 but not sure if I buy a windows 7 oem for system builders (ultimate version) if it will work correctly and activate. Yeah I know about bios mods, etc. This is for a business customer and it would be super to use a bios mod. I am just looking to switch him from enterprise (I was dumb and installed this thinking it was professional) to ultimate. I know this is possible with a retail version of ultimate (using the windows downgrader on addictive tips website) but just not sure how the oem key will change anything. I need this to be a legit copy of windows (again, its for a business). Any help? (yeah I know I can reformat, I am looking to avoid that).