When I play in fullscreen mode, the game gets stretched to fit the widescreen monitor.
Is there a way to get the image unstreched in fullscreen mode or should I just play in windowed mode?

Try fiddling with resolution in the configfile and keep aspect at original/default.

This is most likely just the way your display options are set - do you have the same issue in other, older games?

If you've got an ATI card, you can change this if you open catalyst control center, then go into 'Desktop and Displays', click the display at the bottom and select 'configure'. Then you can choose to preserve aspect ratio.

I don't know how this is done with an Nvidia GPU, but with Intel there's a quick right-click option for it in the system tray icon.

Changing fullresolution to default worked.

Thank you.

You're very welcome :)