here is the deal about the server client programming which is port numbers and their limit its about 65 thousands. I know its not a really big number about if you are planing to serve counts more then 65 thousands.
here is the solutions about it. iocp and p2p networking. I am reading both of those big topics. I think if you are planing to do something big p2p will be the real solution. at least throwing bandwidth of the server to client its easy way to go with p2p. I read jxta and I can say that its absolute solution about java and server part. there are some problems about .net and c# part but. in developing games in this situation its acceptable to build a applet for it :)