just type net send bill..........where bill is other pc's name or its ip.....no domain name......and also check that messenger service is running on both the pc or not......and also check the firewall if necessary....
message must be in inverted comma. Messenger service has to be enabled in order to receive message. go to administrative tools in control panes > Services > find messenger. Double click it and set startup type to automatic. by default it is disabled.