What do I need to do to add an item to the right click menu for files with certain file extensions, along with sub menus?

An example would be adding items to run Python files (.py, .pyw, .pyc) with a specific version of Python, so the menu for a .py files would look like say:

Open  
7-Zip >  
    ...7zip stuff
Run >  
    Python 2.5  
    Python 2.6  
    Python 3.1  
Edit >  
    IDLE 2.5  
    IDLE 2.6  
    IDLE 3.1  
various other items