Thanks to everyone for their input... your open and honest reply's are most helpful and appreciated.

To answer a few questions from the above posters....

-- I've never driven in Japan before. I've driven in numerous countries, including the UK so the opposite side stuff doesn't bother me all that much.

-- I don't plan on getting right off the plane and into a car. I'll probably wait two days and stay in Tokyo and then hit up a train to a yet to be choosen outside area where I can pick up a car and avoid the metro traffic and confusion.

-- I understand that the trains and busses are great aspects of travel when abroad, especially in Japan however I'd like to take a trip to the places that aren't serviced by either and see some of the not so touristy spots.

-- I'm also cool with getting lost and totally fustrated. I'll be going over in Dec or Jan, so I'm expecting the conditions to be less then favorable for a nice stroll behind the wheel... if it is crappy weather, then I'll just do the train thing but if luck is with me then I'll do a bit of driving.

Thanks everyone and keep the input coming, it's really helpful.