If you want a good view of the meadow where the kids learn Do Re Me, go visit the ice cave at Werfen.
The Sound of Music tour company (Panoramic tours) had tours that take you to that ice cave.
Just outside the cave, if you look to your right, towards Salzburg, you will see the castle that is the background of the meadow in the movie. I believe the beginning of the Sound of Music was also right near there. Here's a picture from the same mountain with the ice cave, but a bit closer to Salzburg. Behind the castle is the meadow.