Only if you destroy the machine. Every Dell comes with a factory repair CD or DVD in the case of Vista. If the system starts to get wiggy, you can always re-image the drive back to the factory Vista installation. Of course you loose what ever is on the partitions unless you burn it to DVD or CD, or a network drive. But if the machine is bad enough, you can recover to factory specs. If the machine is still acting up, then you call Dell. You don?t tell them you had XP on it. A word to the wise, if you ever do end up having to re-image a disc to factory or any other image. Dell stores a hidden partition on the disc with recovery information. If you use a utility like PARTIMAGE (PING) to delete the partitions, you may have issues getting a factory image back on the machine.
Where I work, I constantly have to reimage Dell systems because we have so many of them deployed and users will be users, and systems end up with nasty viruses, or corrupted MBR's, whatever the case, but the Image I restore was made from a factory installation and always puts the utility partition back on the system.
You may want to consider using PING or because it is Freeware, and works very well. But if you ever start a project like changing operating systems, it is very wise to make an image of the drive before you start. This way if things go wrong, you can restore the drive back to its original configuration.