Is there any information on writing own protocol base on UDP on internet? I have seem Parsec network architecture, and is there some articles or information that have more clear explanation? I only able to find informations on TCP and basic socket stuff. Thank you! I heard Directplay is simple to use. But is it really suitable to handle a server of around 60-80 people? In case if only doing buy/selling and chatting.

Yeah, that is/was my problem as well.

Try http://www.ecst.csuchico.edu/~beej/guide/net/html/ for more info on socket programming.