Getting There
From the Airport
Munich Airport is 28 km (18 miles) northeast of the city. There is a shuttle bus to the city centre every 20 minutes. The journey takes around 45 minutes.
If you prefer you can take one of the two 'S-Bahn' urban trains, the S1 or the S8 to the main station (Hauptbahnhof) or directly to the nearest station to the Oktoberfest, Hackerbrücke. These leave the airport every ten minutes with a journey time of approximately 40 minutes.
From the Train Station
There are several 'U-Bahn' underground trains which will get you to the Oktoberfest site - The U4 and U5 (get off at Theresienwiese or Schwanthalerhöhe) and the U3 (Goetheplatz). A day ticket will cost you €4.50. The underground runs until 1 a.m. during Oktoberfest (2 a.m. at weekends).
There two tram services - the 16 and 17 - which stop at Hackerbrücke.
The local transport company MVV-München have produced a useful guide on getting around Munich during Oktoberfest. You can download it here (pdf 115K).