Hi! As the game offers no widescreen support, how could I play it letterbox? I mean, simply add to black bars to the screen and stop the stretching?
As wormholewizards said, try looking for an option to change your monitor from 16:9 to 4:3.
I was searching around the internet for hours looking for a way to do this but I never managed to get it working while keeping a 16:9 resolution. Luckily my LG monitor has an option to adjust the aspect ratio, so I just set the windows resolution and the game resolution to 1024x768 and then changed the aspect ratio of my monitor.
It worked like a charm.