Problem with keeping track of threads.

I'm writing some software that opens multiple instances of a single class in
new threads. I need a way of keeping track of all these class instances in
some kind of collection. I'm basicaly writing an MSN Messenger like
application. The threads being, in this case, the chat windows. I would like
to be able to access the various referances in a similar way to the
following if it can be done...
convoThreads["oj******@hotmail.com"].someFunctionInTheClass();

Has anyone got anyideas how I can do this?

Thanx Josh