Try this in Snow Leopard:
01) Get Info on a typical .mov file.
02) Set "Open With" to QuickTime Player 7. (which will be in your utilities folder...)
03) Hit "Change All".
04) Watch the Open With pulldown magically change to QuickTime Player Launcher...which will launch QuickTime Player (X)...sigh.
What is QuickTime Player Launcher? It's an application INSIDE the QuickTime Player 7 app. Right Click on it so Show Package Contents to see it. Then if you want, do that again on QuickTime Player Launcher itself.
What does it do? I have no idea other than seemingly prevent a Snow Leopard user from opening their movie files in something other than QuickTime Player (aka QuickTime X). Seems a little heavy-handed to me coming from Apple.
Here is a thread about it:
Setting .mov files to play in QuickTime Player 7
There is a workaround but I have no idea how "safe" it is.
01) Right-Click on QuickTime Player 7 in your Utilities folder and Show Package Contents
02) Goto Contents>Resources and locate "QuickTime Player Launcher".
03) Right-Click on it and select Compress "QuickTime Player Launcher". The resultant .zip file may appear on your desktop because you probably don't have Write permissions to this folder. Just drag it into the folder and Authenticate when it asks you to.
04) Drag (or highlight and Command + Delete) the original QuickTime Player Launcher to the trash. Authenticate if needed.
05) Empty the trash. (Command + Shift + Option + Delete)
Now, Get Info on a .mov (or whichever) file and tell it to Open With QuickTime Player 7 and Change All and then all of those files types should (so far for me) open with QT7.
The only issue you may see are some messed up QT icons in the Finder, either blank or the generic Unix app icon. Possibly because the OS thinks QT now has an unregistered extension.
I'll update this post if any weirdness happens.