Skip probably is the best place.
If electricity bills don't scare you there's the option of networking them and using it as a small cluster. It'll still be slower than a modern computer, but it'll be interesting forcing them to work together. Could fold on the end result, probably be the first person to run the client across 15 pentium 1s
I believe clusters work by running a single main computer which offloads processing jobs to the rest of the computers, would seem to be the obvious place for the P3
1. Re-badge to Pentium 4
2. Ebay
3. ????
4. Profit
MW