XP install on Panasonic Toughbook

I have a Panasonic Toughbook Im trying to re-install windows XP Pro. I didnt have the install key but I found the unattend.txt file on the cd that has the install key in it. When I put that key in Iget the invalid key window. Any ideas or pointers on how to get through this? Ive already started the install obviously and now I cant install anything on the system so far because I tried my home version and I get the wrong CD entered window.

Thanks in advance!