Sounds like he's trying to muscle you into getting Vista, being that he's expecting you to not know enough to know he's feeding you a line of bull.

As ratscloset said, there shouldn't be anything hardware-wise in any mass-produced computer that would prevent you from installing XP onto it (I don't think there are any Vista-specific components being used for any but the most powerful systems, but I could be wrong).

Though, if you want to install over Vista, it would be better to do a full reformat of the main hard drive (or all if there are multiple, just in case), and then install XP on that clean disk.

________________________________________________________________

If you're joking that's just cruel, but if you're being sarcastic, that's even worse.