DELL

When you buy a Dell PC system configured with the Windows Vista® BONUS program, your PC will come loaded with Windows® XP Professional pre-installed. With the BONUS option, you can transition to Windows Vista® when you’re ready. Your BONUS Kit will include a Windows® XP Professional back-up CD which will allow you to re-install or transition back to XP from Vista if necessary plus a Windows Vista® Business or Ultimate installation DVD. Transitioning to Vista is entirely your choice. Windows Vista® BONUS gives you the opportunity to run the XP OS for as long as you like. Dell will provide support for both operating systems on your PC throughout the limited warranty period. By selecting this offering, you accept the terms and conditions of the Windows Vista® Ultimate License (available here) or the Windows Vista® Business License (available here) and grant Dell permission to install Windows® XP Professional on your behalf.

Source : http://www.dell.com