How to find another computers IP addres?

I have linked my computer to my friends using the following set-up:-
We both have 10mbits TCP/IP Ethernet network cards, and we are directly linked together.
Is there a way of finding the IP address of the other computer so that we can comunicate or is there a program which allows us to do this anyway.
Microsoft Netmeeting requires both computers to be running it and that we know each-others IP address but this isn’t possible without having to physically walk around the house. Is there a chat program we could use.
Many thanks