That is intresting, but I would not [censored] with it. It would no doubt make the downloads much slower than a regular FTP server.
I am not sure your friend will be able to access the FTP server if it is behind a router. This presents an IP issue. I have no doubt there is some way, but I never figured it out.
As far as using a crap computer. That is what most of us do. A 486 would work.
But pentium II would be ideal. I am telling you.. Linux distro with apache is your easiest bet. You could set up multiple FTP logins to various directories. In other words you could have your own private FTP folder and your friends get thier own. It really isn't that hard to set up. Might take you a whole 30 minutes.
I recomend Linux Mandrake if you are new to it.
http://linuxiso.org/distro.php?distro=29 Some prefer Red hat fedora
http://linuxiso.org/distro.php?distro=64