If you are asking the question, then solving the problem is probably beyond you. However I'd suggest reading:
TCP/IP Illustrated volume 2 - Richard W Stevens
Internetworking with TCP/IP Volume 1 - Douglas E Comer
The C programming language - Brian Kernighan and Denis Ritchie
The C++ programming language - Bjarne Stroustrup
and something good on programming graphical C and/or C++ on windows.

Once you have read the above books and understand them, then start reading up on the different protocols used for P2P networks. Have fun.

regards
David Cameron