What is the model of LCD? Each LCD has a native resolution it prefers. You can set it to a different resolution but the LCD itself has to scale it to display it.
It sounds like you might have a widescreen LCD. 1024x768 is a resolution for the 4:3 ratio screens. Widescreens are (if I remember right) 16:9 or 16:10.
Either do a search for your model or post it here and that should tell you what resolution to use. If you think your graphics card can't handle it (it should but don't know how well), you'll just need to adjust the detail of the graphics.