Flake: The TMediaPlayer in Delphi (7) doesn't support MP3 files. The ShellExecute will let you open/run any file as long as it has a recognized extension. for Example:

ShellExecute( Application.MainForm.Handle, nil,pchar(FileName), pchar(Params), PChar(DefaultDir), 0);

So, if you passed in the name of the MP3 file into the varialble "FileName", this would execute the default action associated with MP3 files. i.e It would load you media player and play it.