Windows Vista - http://www.vistaarticles.com
Windows cannot Determine if another Operating System Exists on your Computer
http://www.vistaarticles.com/articles/273/1/Windows-cannot-Determine-if-another-Operating-System-Exists-on-your-Computer
By 
Published on 12/10/2006
 
Receive the following error message in the Install Windows dialog box.

Windows cannot Determine if another Operating System Exists on your Computer

To resolve this problem, edit the Boot.ini file to correct the entries that are not valid. For more information about how to edit the Boot.ini file, click the following article number to view the article in the Microsoft Knowledge Base:
289022 (http://support.microsoft.com/kb/289022/) How to edit the Boot.ini file in Windows XP

When you try to install Windows Vista, you cannot select the Upgrade option. Also, receive the following error message in the Install Windows dialog box:

Upgrade has been disabled

- Windows cannot determine if another operating system exists on your computer. Try repairing the boot configuration, and then begin the installation again.