Doesn't work that way Extatic.

The XP license you purchased with your dell is an OEM license which means it's only good for Dell. That's it, end of story, thank you come again.

Now if you purchased a retail copy XP (box product) you can transfer XP from one PC to another, that's something different from OEM.

In summary, your only legal option is to bite the bullet and purchase the full version copy of XP.