Is there a way to control stretching?

[sickstylishsteve]

I have a 16:9 monitor, previously i've played games at 5:4 monitor on 4:3 res.
Since i've swapped to 16:9 i noticed a few differences in aspect ratio. Playing 4:3 res on my new monitor it seemed more vertical than on my previous one. Back on 5:4 1280x1024 if i played on 4:3 1024x768 it stretched from 4:3 to 5:4.
So my question is... Is there a way to control how much of image is being stretched and how small black bars become? Is it possible to somehow run 5:4 1024x768 on 16:9 monitor? Also does the size of the screen matters on this?

P.S Running 4:3 1152x864 on 16:9 monitor unstretched gives the exact same feel as 4:3 on 5:4. You can try comparing 1152x864 to any 4:3 resolution on 16:9 monitor to see the difference in black bars.