Yes - put all the files from the plugin pack in the 'plugins' folder.
The SDK has some details of how to find out about AC3D's internal commands, as well as a couple of programs for externally controlling AC3D.
If you enable File->settings->advanced->allow-socket-commands, you can telnet to a running AC3D and send it a list command to get a list of all available commands.
e.g.
telnet localhost 1655
ac3d list
This will list all the commands, their parameters and a short text description.
Andy
You can edit the files in the TCL folder to change the UI. If you want to add extra functionality without editing them, make a patch.tcl file in the tcl folder - this will be run when AC3D starts.
For more info about TCL/Tk, see
www.scriptics.com
Andy