How to Uninstall Windows 7

If Windows 7 was installed over an earlier version of Windows...

Windows creates a windows.old folder which contains the previous Operating System and personal files.

Follow the steps outlined in Microsoft KB article 971760 to restore from the windows.old folder. http://support.microsoft.com/kb/971760/

If Windows 7 was installed on a blank hard drive...

backup all personal data

insert either Windows XP or Windows Vista OS install CD and perform a clean install (not an upgrade).

For more info on a XP installation: http://support.microsoft.com/kb/316941/

For more info on a Vista installation: http://support.microsoft.com/kb/918884/