Let us know how it goes! It's a great machine and it would be absolutely tops if you were just hosting plain HTML files with AppleShare IP 6 (there's almost nothing to compromise in system 9) or if you were doing it to mess with Mac OS 9 networking, and it would make a great bridge file server.

Mac OS X is both going to be very slow compared to a minimalistic linux or BSD installation, and be very problematic, security-wise, for a public web server, especially with PHP/SQL and friends.