One IBM PC
Assuming Ethernet adapters available: it might make a firewall, vpn client to connect your network to a remote site, small mail server, network music jukebox, static web page server, print server, ...
The key here is that it will provide a decent platform for anything that does not require heavy lifting. If you want cutting-edge graphics or fast processing, this platform is not adequate.
As a desktop machine it may serve: if you want to browse, do web based email, minor document editing, ... Again, things that allow you to use a much more conservative desktop than gnome or kde, and only at a relatively low resolution. For such use the speed may not impress, but it will get the job done. I bet it would run CrunchBang well. Heavier distributions should run (XP did), but the performance may not be what you are used to.
You have a nice little platform there. Certainly not a high-end gaming machine, but a capable little desktop. While slower than the new machines, it does have some muscle and should be put to use.