Great information guys, thank you very much for your help.
I tried system restore first because it was the least difficult for me, and I thought it might do the trick. However, it would not complete the task, actually the message was that it could not be restored to the restore point that I chose. I tried three different restore points, going further back each time until we were well before the problem started, all of which failed. I never saw that happen prior to this.
I left before the final restore attempt had been completed, but my friend called afterwards and said that it also failed.
Tomorrow I will try deleting the network card drivers and restart Windows, if everything works according to plan, he can put the files on his other computer so he doesn't lose them.
At the very least he now understands why he needs to backup his files from time to time. I learned that the hard way, more than once.
If this fails then we'll look for a cheap HDD and go that route. The Linux CD may be a problem for us to get ahold of, or use, that may be a little beyond my skill level, but thanks for the suggestion.
Thanks again to everyone, your replies were excellent, and very informative.