full screen compatibility

i previously installed an emulator to run an old DOS program.. after i
was finished with it, i uninstalled it from my drive. i have a wide
screen monitor, and current resolution is 1440 x 900.

now, when i run full screen programs, that run in for example 800 x
600 mode-it does bot stretch to full screen. now when a program that
is supposed to be full screen launches, it only takes up a portion of
the screen-and the "desktop surface" is reduced to a window that is
800x600 large.

how can i reset the value so that full screen applications actually
stretch to true full screen? any help is greatly appreciated!

thanks!
.