Shari DCK,
If the XP on the old lappy is an OEM license that came preinstalled on the laptop, then according to the terms of the license you are not permitted to move that license to any other computer.
On the other hand, if the XP that was installed on the laptop was a retail license, which would have been separately purchased in a pretty retail box, then you are permitted to move that license for XP from the old, dead lappy to a new computer.