Description

 This is the upgrade version of Windows Vista Ultimate. An upgrade version allows you to install a new OS over and existing OS. This means that all of your setting, programs and files will not be wiped.

However, only certain versions of XP can be upgraded to Vista Ultimate. 

Go to this site to see if you can upgrade to Vista ultimate. Unsuitable versions require a clean install.
  
I assure every sceptical person out there that this is real!