Lets face it, if you use a beta OS on your main computer you are taking a risk with your computer and your data.  Not only is this so, but whenever you move to the next version of an OS you should do a fresh install.  Of course, in the real world, a lot of us recognize that Windows 7 beta is more like Windows 7 free trial.  The OS is suitable for daily use and any issues can generally be worked around.  The main exception is for web developers who insist on testing for certain versions of operating systems and browsers, those dirty guys (warn and allow it to work if it can, don’t block and complain).  If you’ve decided that its worth the risk to use the beta on your main PC, or all of your PCs for that matter, you probably also don’t mind taking  your chances with upgrade installs.  I hold this view, although Microsoft differs and many so called experts believe you should always back up your data and then do a fresh install.  Unfortunately, since Microsoft doesn’t support upgrading the Beta of Windows 7 to the Release Candidate, and probably from there to the final either, they cripple the install image by making it check the Windows version, then complain about not being able to upgrade pre-release software and forcing you to end the install.

If you’re reading this you’ve probably been looking for a way to force the upgrade, which is the purpose of this post.  To force the upgrade simply follow the following steps. 

1. Burn the Windows 7 RC1 DVD or mount the ISO image.
2. Copy the contents of the DVD or ISO to your hard drive in a folder (windowsdvd for example).
3. Browse to the sources directory in this folder and edit the file cversion.ini (in Windows 7 right click the file and click edit to open it in Notepad)
4. Change the line MinClient=70xx.0 to MinClient=7000.0
5. If you’d like, you can now burn the files back to a DVD to install from disk, or you can simply install by running setup from the folder on the hard drive

An image below illustrates the process.  Beware though, Windows 7 will complain about things like needing you to reboot before it can install, or programs that you must uninstall before running setup.  You’ll also notice a difference in install time.  With the fresh install, in essence, a precompiled image of Windows is just blasted onto the drive and then configured to run on your hardware.  With an upgrade,  the process will take hours on most computers.  The question then is what is the advantage of the upgrade over a fresh install.  You don’t have to worry about reinstalling, and possibly reconfiguring, all of your programs.  This in itself can save you the time you lose due to the upgrade.  In addition, if you have your computer customized exactly to your liking you won’t have to lose your settings and set them up again.  You don’t have to worry about downloading wallpapers, setting up email, recreating favorites, downloading widgets or even pinning items to the taskbar or start menu.  Experts will say to use the Windows Easy Transfer tool, but I’ll add that I’ve seen that tool run for hours before and then fail on some random file or setting.  Upgrading is safe enough.  It is a good idea to use the Easy Transfer tool for a backup of your settings from time to time, but in general I say if you’re willing to run a beta OS on your main computer, you’re willing to risk an upgrade failing and having to do a clean install.  I’ll say that on my underpowered Celeron laptop and my speedy desktop the upgrade went off without a hitch, with the same said of my room mate and his computers.  You’ll want to stagger the upgrade though so you still have a usable system.  In my case, the desktop took about 6 hours to complete due to a bios defect which causes me to have to manually reboot my computer whenever I have an external hard drive attached.  In that case, I wasn’t paying attention when it was time for a reboot each time.  The slow laptop upgraded in about 4 hours since it had no trouble rebooting on its own. 

Here you go.  Give it a shot.