I have a full ( not upgrade ) genuine key for windows 7 ultimate. Can i use this key to upgrade from vista home premium, or is it only for clean full install? Also i don't have a CD, so what other way can i get it.
Yes. If you want to confirm, go to microsoft.com and look at the Windows 7 page. You should be able to confirm easily. In general, you can upgrade from a lower version of one Windows product to a higher level version of the next Windows product, with some exceptions.
From a MS support forum, I found this:
If you are running consumer editions of Windows Vista such as Home Basic or Premium, you can only upgrade to either Windows 7 Home Premium or Ultimate.
Also, you cannot do downgrades, which means, if you are running Windows Vista Ultimate now, you cannot downgrade to Windows 7 Home Premium. You must do logical upgrades:
Windows Vista Home Basic > Windows 7 Home Basic, Premium or Ultimate
Windows Vista Home Premium > Windows 7 Home Premium or Ultimate
Windows Vista Business > Windows 7 Professional, Enterprise or Ultimate
Windows Vista Enterprise > Windows 7 Enterprise
Windows Vista Ultimate > Windows 7 Ultimate.