It's really pretty easy. First, remove the ashtray and cigarette lighter. Then pry out the panel around the whole assembly starting from the bottom outside areas and working upward. Then unplug the modular connectors for the lighter and the lights. This will expose 4 screws that hold the raido assembly in to the dash. Remove them and slide the radio forward. Now remove the antenna connector and the modular connectors from the back of the radio and you are done.
This site might help you as it has some good pictures, but will cost you $4:
http://carstereohelp.net/Str/Toyota.htm
Mike