Sherry,

At any time, you can bypass an application's self-association with a file extension (such as .mid) by setting Control Panel / Tools / Folder Options / File Types / Registered File Types / MID. MID is the .mid file extension for MIDI files. This is a way you can check up on which application has the official last claim to a particular file extension.

There is also a way to see and change this information in the Windows Registry; but there is no good reason I know of for bypassing the Control Panel.

Cheers
-- Mark