Check this page
For NTSC, the picture occupies approximately 480 of the 525 scan lines. For broadcasts the portion of a scan line that is visible can hold up to about 440 dots so a grid 480 high by 440 wide represents the maximum amount of picture detail possible.
So no its not 800x600.
Also check this page
which includes more info.
So unless your running in HD you wont get anywhere close to what a computer resolution can do.