XP is very picky but, it is the computer configuration and product key number that is the most important for activation. Are you including all of the original CDs?

Many older versions of Microsoft's software don't require activation so transfering ownership from one person to another isn't a problem.

I know with Dell, you can transfer ownership if you sell or give the computer to someone. Whether that is really necessary, I don't know. But each time I sold or gave away a Dell, I transfered ownship to the new person.