Background Image not displaying right on Widescreen Monitor...

[nju0843]

Well the title pretty much says it all.

I am developing a windows app for a friend.
The window takes up 800 x 600 pixels on the screen.
The image is 800 x 600 pixels, everything displays just fine on all
4:3 standard resolution monitors.

On his monitor it shows the whole image but the window
appears to be smaller than the window on his screen
because you can see that .net is trying to "tile" the image.
On the right side and bottom side of the form I can see the
image "starting over".

What could be the problem?
What considerations do I need to be taking when developing an application
for widescreen monitor compatibility?

Thanks for your time,
nju0843