how to play warcraft in 4:3 aspect ratio

[Mirage]

Why should it?

I always thought it was a monitor function to not stretch non-native resolutions to fill the screen distorting them in the process, and not a driver option (beyond correcting the resolution used), unless I'm understanding the problem wrong here :p

Many monitors do not let you change this in their OSD control panels, therefore many video card drivers can now "override" it by upscaling a lower resolution image to the native resolution of the monitor. It is with this feature you can make the display drivers keep the aspect ratio of whatever you want to display on the monitor.