Hello,
It is hard to write a decentralised p2p network client if you are inexperienced in programming, trust me, I'm writing a Gnutella client for over one year now and it still sucks (www.darkalien.com / http://www.sourceforge.net/projects/suicide )

However it may get you started if you check out some LimeWire source or just read up the protocol specifications on http://groups.yahoo.com/group/the_gdf/files