I have a Dell desktop. It supposedly has Vista and XP on it. How can I use Vista without installing with disk?

The computer came with an install disk for both XP and Vista as dell's usually enclose another install disk, and I was just wondering if there was a way to start using Vista without installing it off the disk because it says "Already installed on your computer".I have a Dell desktop. It supposedly has Vista and XP on it. How can I use Vista without installing with disk?If it says that it is installed maybe you are already using vista. Chances are the reason it comes with both xp and vista is because the vista is an upgrade version and not the stand alone version. That means you would have to install xp first then install the vista upgrade. If you right click on computer from the start button it will tell you which version you are running.