If you already have an operating system on one of those computers, it would
be less expensive to purchase an upgrade version of XP Home Edition than a
full license. The upgrade version can be installed clean as long as you
have qualifying media. You only need to have the disk for your previous OS.
It must be an actual version and not a recovery CD or some other customized
CD sometimes supplied by PC manufacturers as such disks are usually not
recognized by the upgrade routine.
Nonetheless, if you have the proper media, you can use the upgrade version
of XP, it will be less expensive, you can install to a clean hard drive and
it is identical in every other way to the full version of XP.