In the netbios lookup you supply 2 things. You supply first, the name or IP for a computer. The name could be a domain name or the name of the computer on your local network. The other thing you supply is a range of Interface numbers that you are to query. The reason is cause the remote computer may have more than one ethernet card, or may have both a network card and a dialup connection. Interface 0 will most probably return, and Interfacee will usually result in a "ncb_lana_num field invalid" which means that Interface doesn't exist - they DON'T have a second ethernet card or additional adapter in use for dialup etc...
Try entering the name or IP of another computer on your network - or enter in the name of your own computer. You'll definately get a response. As for entering remote people's IP's... here's some possible reasons you don't get a response (command timed out):
They are behind a router
They are using a software firewall
They don't have "Client for Microsoft Networks" installed
They aren't running windows
"Now what I need to know, is will this command work if sent to macs? is there a way to send one if not logged on to messanger or to a computer without messanger?"
There is a software package that will allow mac's to communicate on a Microsoft Network. However I do not know if it comes with Messenger. It probably does. Usually however, it is not installed.