The Sin Demo shipped with a built in config file (madcatz.cfg). This config file has some of the lines commented out, The commented lines are the weapons that are not available in the demo. If you would like a copy without the commented lines grab this one. From the console you can type in "exec madcatz.cfg" or edit your autoexec.cfg file and add the line "exec madcatz.cfg" to execute it every time you start the game.
If you are using the Panther or the A3D you can edit the madcatz.cfg file to bind the just keys you use. You can even use your Quake2 Config files although you will need to edit the weapon names and possibly some of the command names.