This isn't just specific to battle.net. I am also using C#. I wanna know how to intercept packets and modify the contents or create my own packets and send it to a server or client. But I don't have the slightest idea how to do that. Would that be done a simlar way a packet sniffer finds packets? I would like a idea how that is done too.

Thanks.

The easiest way to do this is to act like a proxy. Tell the game to send the packets to you, and you send the packets to the server. You will have the connectoin to the server, and the game won't, so you can add/modify/drop packets as much as you want.