Ed Felten Has Written A P2P Program In 15 Lines Of Code!
He wrote it to prove the point that this stuff can't be regulated. Now the code is written in Python and I can't read it, but it just shows how simple a P2P program can be. Hell every program could be a stealth P2P program looking at this since the code is so small.
Actually it would be nice to have this in .Net so I could have a go.