Send it to Archeology department
Duh
Better think before you post lad
As for an old P3 machine, you can easily use it as a server. Install a light Linux distro, such as Slitaz or even Arch, or Debian with IceWM or LXDE or OpenBox, etc. as DE or even text mode. You can host any kind of server such as a web server, FTP server, or game server such as Urban Terror 24x7.
There are tons of more uses too, you can use it as a media machine, connect it to your home theater and it can be used as a media player. Use GeeXboX for such stuff.
Moreover it can run 24x7 as a torrent box, as you can fully use your bandwidth for downloading and seeding.
There are plenty of uses of an old machine such as this. Just need to find how to use it.