Windows 7: Activate Windows 7 with OEM licensing?

I've recently installed Windows 7 Home Premium on an iMac using a friend's disc and product key. I however have not activated it yet. So my question is, if I buy the Windows 7 Home Premium OEM version, can I use that to activate the Windows I've already installed without having to uninstall and install it again with the proper disc?

The new key should work...

Any COA sticker key will do.

Okay, thanks! That's great to hear. So two more questions-
1. Since I'm shopping for Windows 7 OEM licensing, some products say "(Branded)" What does a "branded" windows 7 mean?
2. If I decided to reformat my hard drive, like, completely erase the partition I've made for Windows on my iMac and reinstall this Windows 7 OEM, will it let me?

http://www.softwaremarketingsecrets.com/branding-software/software-branding-introduction/

Do NOT use 'branded' disks - they are either counterfeits, stolen, or OEM_SLP activation which will not work on anything other than the original PC.

You should not be using OEM licenses in VMs- you run the risk of having re-activation disallowed if the virtual hardware changes. You need to use Full Retail Licenses for VMs.

If you insist on using an OEM DVD, please read this: Clean Install : Factory COA Activation Key

A clean install will wipe your hard drive.

On a personal note, I agree with Noel. I think you're better to use the less restrictive retail version of Windows, which you can transfer to a new computer after you've uninstalled it from the old one.

Yes, I've realized the hassle of buying OEM so I decided to just get the full retail version. I was just trying to find a cheapest way to buy Windows 7 and I've learned that if the price looks too good to be true, it probably is. Thanks!

You can use an OEM, but buy it from a reputable place like e.g. Newegg. I use their OEMs all the time with no problems. A lot cheaper than retail.

There's a world of difference between 'can' and 'it's a good thing'!

OEM licenses are not transferable to a new machine (even a new VM) under any circumstances, so if this one breaks even 2 minutes after activating an OEM license there is NO way to transfer it to another machine.

ALSO, the OEM System Builder License - which you agree to when you open the pack and BEFORE you start the install - states specifically that installations MUST be for a third party. MS could theoretically prosecute anyone who installs an OEM license for their own use.

OEM Licenses have no support from MS (OK, even retail license support only lasts for 90 days, but those 90 days are critical for most people) - the System Builder is expected to provide the support - which is another reason that they are so much cheaper than Retail licenses.