You cannot purchase OEM software - it comes with the computer when purchased from a re-seller.
Are you sure it was OEM you purchased?
I agree with Kristopher T
Secondly for upgrade you need full version of Windows 7 Official DVD
Hi. My name is***** you for your question and the opportunity to assist.
An OEM disk should work just fine. You'll have to boot from the disk and do a clean install
of the operating system. It won't install if you're logged in to XP and run the setup from the disk.
What's the brand and model # of the computer you're trying to do this on?