I've created a Flash video of how I did it in my Notes 7 client. This might be different for older versions of Media Player and Notes.
Media Player v10 does not need any programming to play the movie.
For older versions and other OLE objects you might need to add code in Initialize event of the Object. In that case the code would look something like this:
Dim workspace As New NotesUIWorkspace
Dim uidoc As NotesUIDocument
Dim handle As Variant
Set uidoc = workspace.CurrentDocument
Set handle = uidoc.GetObject( "Movie Player" )