I want to enlarge/reduce the size of the chat room window.

Use a chat room macro. You'll find an example in standard.tpl Don't forget to assign you macro to the appropriate chat room(s).

For JAVA chat, this is simply changing the HEIGHT and WIDTH settings for the applet.

For HTML chat it similarly is just changing (adding) the HEIGHT and WIDTH parameters of the TABLE tag (and where appropriate the other TABLE subcomponents).

As with any macro, remember to reset your cache for the parameters to take effect. ALSO! Browsers tend to cache the JAVA applet and its parameters, so be sure to PURGE your browser's cache (or your browser's JAVA compiler cache) of all content first, then reload/refresh.