Q: I am managing a lot of OEM licenses in my computer. Now, I want to redeploy Windows on the same machines. Is that even possible?

A: Yes, you're legally allowed to reinstall the products on the same machine. However, you can't use the pre-activation key as this is a one-time-only activation method used by OEMs such as Fujitsu, HP or Dell to spare users the trouble of activating Windows. There are, of course, ways to extract the license keys and the authentication files (.xms-ms), but OEMs see this as a reverse engineering and thus an illegal license retrieval method.

Q: I bought a copy of Windows 7 Professional (Upgrade), but I want to perform a clean install on my XP machine. However, when I try to enter the key it says its invalid. I want to start off fresh, so what can I do?

A: Here's an official, yet unorthodox, method to clean install using an upgrade media: Install Windows 7 using the clean install method, but leave the product key form blank. You can still continue. Once you're done installing, insert the Windows 7 Professional DVD again and run the setup. This time, it will ask you if you want to upgrade or perform a clean install. Pick "Upgrade". While you now have to wait through another installation, you are essentially running a legal upgrade version that you can activate easily.