- Hypothetic: pretty outdated but useful to start..
- MsnPiki: a wiki with updated content
- MsnFanatic forum: a forum you know :P, you can find interesting threads there
- Siebe documentation: great resource for p2p, I don't know why he removed it (using internet archive)
- imfreedom: new but pretty empty
- some useful msn msdn links :D
Orfeo C recommended SocketSniff, I did't tested it, but it may be useful for someone