[Marc Lucas]"Wanting to select a fixed size with the Marquee. I input my pixel area size but everytime I try and select on the image the edges of the image become selected and not the actual size I specified."
Sounds like the image is smaller than the size you're specifying. Are you certain that you're giving the fixed size in pixels (px)? If the field is set to another unit this may lead to unexpected sizes.
If it's still not working an alternative would be using the Select > Transform Selection function and entering units in the horizontal and vertical scale boxes. These default to 100% x 100% but you can enter pixel or inch values in the boxes simply by putting 'px' or 'in' after the value: "256 px" for example.