From Munich, there's a very good transfer company called Four Seasons. See their webiste at www.airport-transfer.com
From Salzburg, there's a transfer company in Kitzbühel called Andi's Taxi. See their website at www.andis-taxi.com
From Innsbruck, the best way is by train as the journey is only about an hour and usually direct. See the Austrian railway's website at www.oebb.at
Click here to see a map and assess a route
the ÖBB website is really good and easy to use: www.oebb.at
When you arrive in Kitzbühel, make sure you get off at the main Kitzbühel station where there are usually plenty of taxis.