Hello, early adopter—your eyes might've glazed over during the Windows 7 launch because you've been on that train for months now. This is for you: how to upgrade that Windows 7 release candidate to a final version, easy.
Basically, copy of all of the files from the retail disc to a folder on your hard drive, pop open the "sources" directory in that folder, and open up the file called "cversion.ini" in Notepad. Change the number 7233 to read 7000 (you're telling it the minimum version that's allowed to upgrade). Save it, and now you can do an upgrade install (hurray no paying for a full version). You might see some slight wonkiness, but Max PC says they've had some "good results" this way. [Maximum PC]