Just got back from Munich. Great fun. Train is simple to use. You can take one from the Airport directly to the Munich City Hilton if you choose to stay there. Costs about $9 and takes 50 minutes. Piece of cake.
One neat side trip if you have a car is to head south about 90 minutes to Oberamergau, the site of the Passion Play. Quite a neat little town with all kinds of shops, restaurants, etc. Nearby is a 13th century monastary (that brews terrific beer). You can also see Garmisch and 2 of King Ludwigs castles (Linderhof and Neuschweinstein) in a very long day.