If a repair boot will actually solve the problem, lend him an XP disc. You can also download numerous boot-and-repair environments (to a working machine) and make a boot disc. I was looking at one the other day; if I find it, I will edit this post.
If that doesn't work and there is enough needed stuff on the machine, consider paying for professional help.
Alternatively, the friend could restore an earlier OS backup. Just joking.
Another thing you may want to consider is taking out the drive, sticking it in another machine that has excellent virus protection, and making a copy of all his files. That way, if the disk goes south during a repair, at least his pictures, documents, and so forth will still be available. This is a good FIRST step.
Here it is: http://www.tomsguide.com/us/pictures-story/332-free-data-recovery-backup-restore.html#BOM_comments
. Download number 13, the boot CD, and you get all of them in one bootable environment. Don't know which one you should try first. Maybe Avira, page 7.