Chatrooms can be created on the fly using the IM client, but they are not persistent. If you want to add persistent chatrooms you have to do so using TIMP.NET Console.
In the following document we assume that users have an IM Address of this type: user@myserver.com
Log-in to the TIMP.NET Console; on the left, under the Domain listing:
When you commit any change, you should always remember to Click on Apply to have the changes applied to the running instance of TIMP.NET; also click on Save to Disk to have the changes committed to the configuration file (so that, if you restart your machine, the changes in your configuration will not be lost.