From the airport you can go to Bad Wiessee by taxi (about 1h, app. 150,- DM) or by train (S-Bahn, BOB) via Munich "Hauptbahnhof" to Bad Wiessee. 
   

The nearest big train-station is in Holzkirchen. You can go to Holzkirchen by S-Bahn or by train. The S-Bahn is going to Holzkirchen at least every 40 minutes. For using the S-Bahn you need a special MVV-ticket for 6 zones. Besides you can use the "Stadtexpress" from Munich Hauptbahnhof (lane 27-35) to Holzkirchen (train towards Bayrischzell or Lenggries). You can use the MVV-ticket also to the train.
   time-tables of "Die Bahn"
   MVV-homepage

From Holzkirchen you can go to Bad Wiessee by taxi, by train ("Regionalexpress" towards Tegernsee/Gmund) or by bus. In any case you can use the bus to go from Gmund (the nearest train-station to Bad Wiessee) to the health-resort of Bad Wiessee. 
 

In most cases you will come to Bad Wiessee from Munich. So from Munich you take the highway A8 ("Autobahn") towards Salzburg (Austria). In Holzkirchen you have to leave the highway. From there you go towards Tegernsee. 
   Bavarian road-informations
   Tank & Rast AG

Gmund is the the first town at the lake of Tegernsee. From here you follow the signs towards Bad Wiessee. At the first crossing in Gmund you have to bend of right to go directly to Bad Wiessee.