Creating your own chat room will take a pretty good understanding of Actionscript and some other backend scripting language like PHP or ASP. A chat room is not the same set up as a multi user game environment. Most chat systems just parrot a textfile back to flash with the use of a backend script. Real time multi player gaming is usually handled with an XML socket connection. There are a few multi game servers available but they usually cost. If all your looking for is a text based chat, try a google search. There are lots of those around...
A mind once stretched by a new idea never regains its original dimensions.
- Oliver Wendell Holmes