The release candidate of 7 was pretty stable but you can’t upgrade directly from it to the final version at least, not without a work around. I should say Microsoft do not support this method.
The Problem
Windows 7 checks whether or not the current version you are running is a pre-release copy, and prevents you from upgrading further. This is the error you might see when you try and upgrade.
Φ You can't upgrade this prerelease version of Windows 7. Go online
to see how to install Windows 7 and keep you files and settings.
The Solution
The solution is to edit a file inside the Windows 7 DVD, which you’ll have to extract to the hard drive to proceed.
A second hard drive, USB drive, USB stick (4GB or more) or network drive would be a good choice.
Once you’ve extract the files, browse down into the “sources” folder to find the cversion.ini file.
Once you’ve opened up the cversion.ini file, you’ll notice that the MinClient line has a value of 7233.0, and since the Windows 7 RC release is build 7100, you can understand why it’s not working.
All you need to do is change the MinClient value to something less than the current build you are using. For the RC release, I suggest you change it to 7000.
Now you can simply launch the setup.exe file from within the folder, and do the upgrade directly or copy the files back to a writeable DVD if you don't have much disk space and proceed from there.
You may see the list of applications on the Compatibility Report screen that probably won’t work once you upgrade. Realistically most of these apps will work just fine. It told me to deauthorize my PC from iTunes which I did, you can reverse it after the upgrade.
At this point, the upgrade should start working, and will take a rather long time.
Important Notes
There are a few important things to keep in mind when you are upgrading to the final version:
The Windows 7 beta or RC releases were Ultimate edition, so you’ll only be able to upgrade to the RTM (final) if you are upgrading to Ultimate Edition.
If you have the time and inclination, you should really backup your files and do a clean install. There are less of any problems and you get the benefit of a nice clean profile.
