Why not contact the company you buy your PC's from (and a few others) and see what they have to offer for new (or refurbished?) PC's that are both XP and Windows 7 compatible.
I am working in a large company that have more than 20 000 computers running Windows XP. They are being replaced with Windows 7 PC's, but this operation will not finish until 2015.
We are starting to run into a problem that new hardware will not be supported by Windows XP. The first issue at the moment is the lack of drivers to Ivy Bridge chipset.
Is there any good ways to install XP on future PC's? Like using 3. party drivers etc? Plan B will be to "re-use" old parts.