To expand upon previous posts... resolution is a physical aspect of your LCD screen. It physically can only display 800 x 600 pixels, no more, and no less (640 x 480 will actually be blown up to cover all 800 x 600 pixels, with a loss of quality by the video card). There is no way to shrink 1024 x 768 down to 800 x 600, as you will then not be able to see some of the data (you can fit a small object inside a large object, like a microwave in a Honda Civic, but you can't fit a larger object into something smaller, like a Whirlpool double-wide refrigerator into a Honda Civic).
This means the tiny dots that make up the images on your screen are 800 dots left to right, and 600 pixels up and down. Your screen is, in essence, 480,000 teeny tiny square panels (800 multiplied by 600) placed together, each only being able to show one solid color at a time.
