XP Pro SP2 Set up – Can’t cancel

I have a legal copy of XP Pro SP2 which is backed up onto a hard drive. During my latest move I can’t find the original. My son in law started to reinstall on a crashed disk. He was able to make a copy of the ‘disk’ onto a CD. But, we can’t find the original keycode. Now, it’s stuck halfway through and won’t let me use a new legal CD. Unless I can come up with the key code I can’t move forward. And, unless I can either move ahead with the keycode or cancel it… the Full copy can’t take its place. How do I A) find the original key code, or B) cancel the install in progress and install from the new disk with a keycode?