Nissan Gallery is in Ginza, and there is Nissan dealership about 10 mins walk from it. Ask the girls in the Nissan Gallery and they'll give you a map.
Sony store, is about city blocks from the Nissan Gallery and well worth a visit.
It looks like this...
The Toyota Megaweb and Toyota Museum & Historic Garage is very easy to find. It's in Odaiba, just jump on the monorail/driveless train thing (Yurikamone Line) and you can miss it (it has a ferris wheel next to it.) Or do what i did, got up very early, did the Fish market thing, then next door to the Market is the Hama Rikyu-Onshi-teien (the Detached Palace Garden), and there's water ferrys that go to Odaiba.
The Ferris wheel and the Toyota Megaweb..
The Fish market is a must IMO, and same with a Visit to Senso-Ji in Asakusa.
I stayed in Shinjuku here,
http://www.nshotel.com/english/index.htm
Oh and Japanese Public Transport FTW!!! All the train lines are color coded, and the all the stations on the lines have numbers....so to work out what stop you want is just look for the number in a colored circle of the line your on.
i.e
http://www.gchicco.com/wp-content/uploads/...o-metro-map.png