Help reinstalling XP

Ok, I'm going to try to explain this from memory as I'm at work and the computer I tried to reinstall xp on is at home. I've reinstalled windows on other machines before with ok success, so I thought I would give it a try.

I originally wasn't going to reinstall windows but this being my teenagers computer I thought it would be better to just give the machine a clean start and get rid of all the crap that they put on it.

I went to reinstall and got to where you decide to reinstall or repair, I chose repair, got so far and it asked me for admin password. No idea what that would be, this was my deceased father in laws machine. So I decide ok, instead of repair I'll just reinstall. So I reboot and get to the choice screen, select reinstall.
Now I get as far as a screen that says, preparing to continue install...... then goes black and does nothing. I then rebooted again, now I get as far as the screen to choose drive to boot from then it goes straight to preparing to continue install....... then goes black and does nothing.

Any ideas except to throw the machine in the harbour? I keep telling the kids to run their anti virus and stop putting crap on the computer but that goes in one ear and out the other.

Any ideas?