Socket Project (getting one of multiple clients IP)

I am making a project for my computer science class. I need to create a multiuser chat program where a user on logon will recieve a request form the server asking for a user name. The server will get the clients username and its IP address. I am stuck on how to get that person's IP address when he begins to enter his message. I know of the inet_ntoa() function but I am not sure how to specify the correct user. The end result upon all the clients screens will be something of the sort:
"wake nate05: what about you?
Rav8Warriors5enS: chillin
Rav8Warriors5enS: bout to do some weightliftin and then study
wake nate05: cool"

Any help is appreciated.

Well I don't know how to do threads, secondly can you not get the IP where activity is taking place?

Ahh that works nicely and thanks for that example on threads. Now I just have to get it to work on good ol Windows :).