Uninstalling Windows 7
Suppose you've tried Windows 7, had your fill, and decided to uninstall it and go back to the earlier version of Windows that you're used to. Providing you backed up your data before installing Windows 7, you can grab that backup and follow these directions to get back to the Windows version you preferred.
Format your drive to remove Windows 7 and make it ready to get a new (old) installation.
Follow the directions for the backup program you used to put the image back on your computer.
Put the backup you made away for safe-keeping — you may need it again, just in case.
If you don't end up buying Windows 7 eventually, you're going to have to go back to your original installation anyway. After one year, the installation will quit working, and it's going to start shutting down after two hours of operation before that date occurs. For that reason alone, it's best to try out your initial installation of Windows 7 on a computer you can afford to mess around on and not risk losing your most important data.