Already made a thread about this awhile ago.
Myth II and vista have an issue where the game sounds will cut out, for example you will no longer hear "game on" or "casualty" nor even "flag captured." You also won't even see the text that normally accompanies these game updates.
Something I found recently though was in windowed mode, not maximized, the sounds remain the entire game as normal. Its extremely difficult to play in an unmaximized window so this really isn't a solution but I thought it was worth mentioning.