Just a though,
If all of the listed options fail, you can drop his HDD in your PC as a slave, boot into your windows XP(the one that works), and copy all of his needed files to a CD, return his HDD to his PC, then reinstall windows on his HDD and transfer the files from the CD to the HDD.
With that method you bypass his bad OS and salvage his files.
If all of the listed options fail, you can drop his HDD in your PC as a slave, boot into your windows XP(the one that works), and copy all of his needed files to a CD, return his HDD to his PC, then reinstall windows on his HDD and transfer the files from the CD to the HDD.
With that method you bypass his bad OS and salvage his files.