Replace Vista with XP

My client has a laptop with XP and likes it, and a fairly new Desktop with
Vista and dislikes Vista.

Can I use an OEM version of Win XP to replace the current Vista?  Newegg
indicates that I must have reciepts for a new MB, CPU, RAM, & Hard Drive.

Any suggestions on doing this?

Replace Vista with XP

Who would require the reciepts,not microsoft..

Replace Vista with XP

First off check that you can get XP drivers for the desktop machines
hardware (motherboard, graphics, sound etc.).

Secondly OEM versions of software are usually sold with a specific piece of
harware, be it a whole "computer" or a hard drive etc. so that is probably
what Newegg is going on about.

It is certaily possible to use OEM or Retail versions of XP to de-Vista the
machine provided, as I said earlier, that you have the relevant drivers.

If the machine is a proprietry brand such as HP or Dell check with the
manufacturer to see if you can purchase an XP downgrade CD for that
particular unit.