Do yourself a favor. Research the movie and Salzburg and find the actual venues you can easily see from town (Mirabell Palace and Nonnberg Abbey). The actual tours are, in my opinion, the definition of tourist traps. They take you on an overpriced tour and show you venues only loosely assiciated with the movie.
Examples: (from Panorama's own website)
Mirabell Gardens: like I said, easily viewable on you own. Right off the street that goes between the Bahnhof and the old town. See the Pegasus statue and the Do-Re-Mi steps. Also the arbor they ran through.
Leopoldskron: this building never appeared in the movie. It was a school at the time, and the owners didn't want the interruption. The crew built a reproduction of the patio next door, and that was where the famous boat scene was filmed. The Captain never lived here; those weren't his "backyard and private gardens".
Yes, I remember the song "16 going on 17" and the kissing scene. None were shot in the gazebo you see at Hellbrunn. The scenes were shot in Hollywood in a sound stage; the gazebo you see was only seen a few seconds at a time in the distance, on the temporary set next to Leopoldskron.
Nonnberg Abbey: it's on the hill with the Fortress. You can "visit" it easily by yourself without a tour.
Salzburg Lake District: St. Gilgen was used in a few panorama shots at the beginning, along with closer Königsee, at Berchtesgaden, which they don't show you. "Scenes of the picnic"? Total fabrication. The picnic scenes, where she teaches the kids to sing, were shot in Werfen, twenty miles south of Salzburg. That's Hohenwerfen Castle on the hill behind them. The scene where you see them boarding the cog train is at the Schafberg, in St. Wolfgang, nowhere near the picnic scene.
The wedding scene between Maria and "Baron", actually Captain Von Trapp, was shot at Mondsee. You can take a local bus from in front of the Salzburg Hbf to Mondsee.