Yeah it was made in 1949 and starred Joseph Cotton and Orson Welles, it took place in Vienna. The story was written by Graham Greene and he based Harry Lime on double agent Kim Philby; though in the story Harry is a black market crook. The 50th aniversery edition is out on DVD but is rather pricey.
The movie's 'Third Man Theme' tune was played on a zither if I remember rightly, and was a real catchy earworm: "Da-da-dah de-dah-de-dah, Dah-de-dah de-dah-de-dah" over and over and over ad-infit-nauseum.