For those who want some background, I can't summarise it any better than this post.
http://forum.live-evil.org/index.php....html#msg11675
Be warned you will be reading spoilers. This gives plenty of historical background.
However to put it in a nutshell this is based of the same real life story that the Sound of Music was based on. At least from the episodes I've watched the story follows the book very closely. You can order it off Amazon.com (it's called "The Trapp Family Singers" by Maria Augusta Von Trapp.
-gumbaloom
PS
As for the how and why I chose it, I came across it by accident and was like OMG AN ANIME BASED ON THE SAME STORY OF THE SOUND OF MUSIC *_*. So well I bought the first DVD and the rest is history. The fact that it was World Masterpiece Theatre helped immensely.