The first steps in a nutshell:
Add a new a/v device under A/V equipment, choose Panasonic for manufacturer, and TVs/Plasma/etc.. for category then 'Add device template'. Give it a name and choose RS-232. You can leave most of the remaining settings as defaults (I'll get you specifics for timings when I get to my core tomorrow), select all the inputs you have on the tv when prompted, set the # of times to repeat commands to 0 (not actually certain if this affects GSD or just IR devices). You'll have to enter the name for a new IR group and select "add ir group". When the device template displays select the "Ruby Internal Commands" and choose Update, this will add the required internal ruby commands that will interact with the GSD device and dcerouter. Next comes filling in the commands.
I'm on a test machine right now so I'll have to grab the GSD code from my core tomorrow and post it. It'd be nice to have someone else test it out, then I could submit it to sqlCVS.