Finding the ip address of another computer on the network?

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http://askubuntu.com – Is there a program which can tell me the ip address of a computer when is connected to my network? A list of names or ip addresses. For example when my wife is on my main desktop computer I can either go on another desktop or laptop and work. However I don't know the ip address of the computer she's on it's dhcp and no static ip addresses. I would like to ssh into the main desktop and work on it. Sometimes I have asked her if I could get on for a minute to get the ip address. From a terminal I do an ifconfig and get the address. I could get it from the router too but that is requires ()