Need help with the Aspect ratio options

Hi everybody!
I'm using Intel 82945G Express Chipset Family. My monitor resolution is 1366x768
So whenever i run a 1024x768 program, two black borders will appear on the left and right of the screen
But now, it expand to the whole monitor instead, make the graphics look 'fat'
I have selected 'Maintain aspect ratio' as below, but it doesn't work

Can anyone help me out?
Many thanks...