I know that I used to have a Windows XP 8-in-1 CD. On this CD, you could install Pro:Multiple Licence, OEM, Table, and Multimedia (and same with Home). In order to install the multiple Licence one, the CD came with a tool that created and validated XP CD-keys. I'm sure if there was such a thing for XP, there was for 2000 - you just may be looking under the wrong name. I forget the exact name for the term used to describe a multiple install license, but that is what I believe you are looking for...

Sorry I can't be more specific.