For a lot of MaximumPC readers, the fuss over Windows 7 launch week might seem a little unwarranted—after all, many of you have been happily running Windows 7 for months now, so what’s so exciting about a retail launch? In fact, if you’re in that boat, the launch poses more of a hassle than anything else, since your free RC version of Windows 7 is closer than ever to shutting down. And when it does, you can't even do an upgrade install of Windows 7, you have to either re-install Windows Vista first, or buy a standalone version of Windows 7.
Or do you? Even though Microsoft’s official stance is that you can’t upgrade from the Release Candidate to the RTM/Retail version of Windows 7, it’s actually possible to do so using a quick, easy hack. This means that you can use the cheaper upgrade version of Windows 7, and do a "Custom Upgrade" to get a clean install. Or, if you don't mind the risk of additional headaches down the line, you can do an in-place upgrade from Windows 7 RC to RTM. Here’s how to do it, in 7 simple steps
Insert your Windows 7 retail disc into your DVD drive. Make sure to put the 32-bit installer disc in if you’ll be installing 32-bit Windows and the 64-bit installer disc in if you’re installing 64-bit Windows. If you downloaded an ISO from TechNet, simply proceed to step two.
Extract all the files from the DVD (or ISO) into a folder on your desktop.
Open the folder you moved the files to, then open the “sources” directory.
Using Notepad, open the “cversion.ini” file.
This file specifies which versions of Windows are eligible to upgrade. Right now it says the minimum client version able to upgrade is 7233 —change this to read 7000 and you’ll be able to upgrade the beta or RC to RTM.
Save cversion.ini, overwriting the old file.
Install Windows 7 using these modified installation files. The easiest way to do this is by following our boot from USB guide . If you want, it’s also possible to create a new installation disc from these files using the free burner ImgBurn . You can find a guide on how to do this here .