I don't think there is a way to force a 16:9 screen to a 4:3 using computer settings. Unless, of course, your monitor has some function to change the aspect ratio.
The only thing that will happen if you do play the 4:3 game on a 16:9 screen, is a little bit of stretching. Some of your "guys" will look a little fatter....
No music problems, no lag, etc...