Old Computers

So I have three older PCs that I'm not sure what to do with... 1 AMD Sempron 3100+ with a gig of Ram, 256MB of Video Memory, so it's a pretty good machine... 1 1.9Ghz Pentium 4, 512MB of RAM, 128MB of Video Memory, and an old P2-400 with 384MBs of RAM... I'm not sure what to do with any of these... so if anybody has any idea, I'd appreciate it...

I'm thinking I could use the Sempron for a Windows Home Server and test it for backups and the like... Possibly use the 1.9GHz for a security gateway... since I'm going to divide my network into two segments, Public and Private... but we'll see... I may just lock down the wireless...