I had a little different problem, but with the same solution I think. My cousins PC wasn't recognizing the DVD-ROM drive because the driver was "missing or corrupt". I insterted the windows xp home cd and rebooted, once it was at the blue screen, and shows you the partitions available to install xp too, I selected the 1 partition and hit ENTER (to set up XP on this partition) and it then gives you the option to hit R to REPAIR this windows xp installation on this partition. I tried using my xp pro cd on her PC and it didn't work, I had to get her XP home disk in order to do it, so I'm not sure if Win XP Pro has the option to repair like that, I would assume so, just didn't work in this case because she had XP home, and my disk is XP Pro.
Hope you get it working.