Kema.. Obviously YOU don't know what you're talking about. If you understood the basic concepts behind TCP/IP, you would know that it works sort of like an address on your house. You can't see the address unless you look at the house. When you're looking at the house, someone can see you from the inside, all they have to do is look.
All that means is, unless you connect to them, or they connect to you, then you will never know thier address without them giving it to you.
*Unless you're on a service which blows and the protocol sends the user's address in packets across the network. But, then if that were happening, your IP address would be available also, again.. refer to the "house" analogy above.