You can use the OEM ver.
The only diff on OE Win 7 vs Retail is in the Lic.
OEM is tied to the MB that it is first installed on. So if you Upgraded the MB you would need a New Lic. If MB dies you are OK.
Retail can be moved and only restriction is that it can only be installed on one computer.
Other diff is uSoft does not provide any troubleshooting telephone assistance for OEM.