How to activate the windows 7 operation system

I had been utilizing the Microsoft Office 2007 Product Key beta version of Workplace, and it converted all of my notebooks up to Microsoft Office 2010 Pro Plus. Now that I've uninstalled it, my 2007 edition won't study them, and I can't locate some thing that will alter them back again. Is it achievable to alter them with out buying Windows 7 Home Premium Product Key?