I Have also tried like Maartin to use the protocol built in in windows, I know that is you send a message using 'net send' to a W95/98-computer running Winpopup, it would recieve the message, and winpopup sending to an NT-computer would make the message popup. This means they use the same... "port" ? which is equivalent to wheter winsock it uses since if tcp/ip is not installed it does work anyway if you have ipx/spx. Microsoft hasn't given me any answer and I guess they don't want to either.