For the sake of XP installation continuity, we can use the default product key inside the XP CD.

You can find the product key by browsing:

<cd-rom drive letter>\i386\unattend.txt

At the bottom of the file, you will find the product key. One of the common product key is

CD87T-HFP4C-V7X7H-8VY68-W7D7M

After finishing the XP installation, you need to activate Windows and use the original product key of the computer.