If your screen doesn't have THE SAME EXACT resolution of the skin then it will have to be resized and it will look "deformed"... You have three options:
1-Set your monitor to 848x480 and use the 848x480 skin
2-Set your monitor to 800x600 and use the 800x600 skin
3-Resize all the JPEG files to 800x480 (i.e. Photoshop) then open the skin in the skin editor and adjust the areas of the buttons and objects to match that size. That's the only way to use 800x480 without looking deformed (short of the author providing a 800x480 skin).