|If your XP CD came from HP, they ususally prepare the CD such that XP installs unattendedly, which means it does not ask for a CD key. The key is in the winnt.sif file in I386 folder on the XP CD, which is used for unattended installation. You can open winnt.sif file in Notepad. If this file does not exist, you cannot install XP unattendedly out of the XP CD.|
Sometimes, unattended install is done through Floppy Diskette. In this case there is a file called unattended.txt on the floppy that carries your product key. Look for a floppy diskette that should have been supplied with your PC.
If your XP install asks for a key, that means your XP CD does not have the key inscribed on it and there is no winnt.sif file. Therefore, you have to buy another key, maybe with a discount.
Hope the above helps.