This has got nothing at all to do with the screen resolution. It's got everything to do with the aspect ratioo of the display screen and the aspect ratio of the video you are sending to it.
You may have noticed that nearly every wide screen TV you see in pubs, clubs, museums etc, is incorrectly adjusted, and that all the people in the on-screen pictures are stretched horizontally.
This is because things are not set-up correctly. Not only is the picture distorted horizontally, but about a third of it is missing! The whole idea of widescreen was to give a picture with more on it. This is especially advantageous for sport etc.
See here
http://www.radiofeeds.co.uk/wide/
So the upshot of all this for your laptop is that you must make sure that the video signal you are sending to your widescreen display, is itself widescreen.
How you do this depends on what software you are using to play your videos. Make sure the aspect ration in the software is set to 16:9, not 4:3.
As far as your desktop and windows are concerned, you will need to adjust your display properties in the usual way.