I have successfully cleaned machines that had 3 or 4 viruses on them, but it often took booting into safe mode, editing the registry, deleting certain files, and running virus programs 2 or 3 times to clean out the remaining gunk. If there are 124 infected files or *gasp* 124 actual viruses on the machine, I wouldn't bother trying to clean it. Even after you have spent hours of your time on it, some infected files may remain and you may have more trouble down the line. Plus, formatting the HDD so that your friend loses all of his data is a good way to ensure he keeps his current anti-virus up to date and doesn't waste your time in the future
And if his ISP blocked him, tell him you can't fool around or he may have to look for another ISP.