Q: How do I open a file saved in a newer version of Maya in an older version of Maya?

A: Go to File > Open Scene > option box. Ensure that "Ignore Version" is checked on. Alternately, in even older versions of Maya that don't have this option, if the file you are trying to open is a .ma file, open it in a text editor (yes, Maya ascii files are just text). There should be three places where the version is stated (e.g. 2011), change those to your version (e.g. 2009), and try opening the file again.

Please Note! There is no guarantee the scene will open and work perfectly. If the scene includes functionality that is only available in newer versions of Maya, chances are the scene won't work perfectly. Maya will give you a nice warning stating this when you open the scene.