<<l was wondering if someone had sold him a counterfeit OS.>>
Easy way to find out...go to Windows Update and employ the WGA tool.
<<Would you know if this machine originally had Win XP Home on it?>>
No way and even if it were possible, it would be immaterial.
I'm living proof that anyone with the ability to read and locate drivers...can install any O/S on any system
. If Vista is on it and the system works, then there probably are Vista drivers installed...which is all that it takes.