I could be wrong, but I think that your OEM copy of XP Home is only legal for the machine it was included with (sucks, but that's the way it is).  Really sucks because I just bought an HP laptop (I mentioned earlier that I was getting an iBook, and I really did want to . . . . but at $1600 + tax for the iBook vs $1050 for an equivalent HP with a free carrying case, I just had to go with the HP).  I will be loading Linux on the laptop and would really like to run the copy of Xp Home included with it on another machine, but I don't think I can, so I guess that's just wasted money (paid for an OS that I didn't want).  Oh well.