Real non tech suggestion..........complete the XP Home install with a generic Home product key, either a friends or a keygen fresh one, and select not to activate. Then boot the XP Pro disc and install over the Home install.
Technically spoeaking, that old Pro disk was probably previously activated, and the product key will not allow passing on an OS to another person.....heck, they don't even want you to reuse your OS on a replacement computer, even if you smash the old computer to pieces with a sledgehammer 🙂
I had a hacked XP Pro install on my old laptop because I couldn't find my Win 2000 Pro product key after a reload and a buddy had the hack handy. I ran into a lot of problems with programs requiring new service packs that Microsoft won't let you install without Microsoft Genuine Give us all the money and no one gets hurt Advantage. I was able to hack away that roadblock but it's tedious and annoying.
Hmmm......I just remembered, when I installed an previous XP Home on a second computer, an allowable laptop per the EULA, I had to call Microsoft and they gave me a new product key and all was well. I suggest when installing call Microsoft and tell them your putting your allowed second copy on a laptop 😉
Paul