I have tried this several times. I completely DO NOT believe that Dark Side of the Moon was composed as a soundtrack to The Wizard of Oz.
Popular music in general, and Dark Side of the Moon in particular, has many key changes, tonal changes, and lyrics which espouse general themes of love, fear, loss, and longing. Movies have many camera, scene, and set changes and also use universal themes of love, fear, loss, and longing.
If you put any movie and music album together you will find occasional coincidences between them. Combining a movie about a girl's dream fantasy (Dorothy), and an album about a acid-using musician who went off the deep end (Syd Barrett), you are bound to find more than the usual amount of coincidences. See this website for some of the coincidences you may see when combining them:
http://www.ingsoc.com/waters/info/oz.html
However, there are many more key and song changes, lyrics, and other aspects of the album that DO NOT match up with the scenes and plot of The Wizard of Oz than there are connections. But the human mind works by trying to find meaning in the world, trying to find connections between everything we experience, particularly when we experience them simultaneously. So we do find connections between the album and the movie. But it is not unique between these two creations.
Try matching up The Wall with Alice in Wonderland. If you want to try dozens more coincidental "synchronicities" between movies and albums then check out this website:
http://www.synchronicityarkive.com/