> when I view the page in Netscape 4 [...], the div looks normal, except for
> a small margin on the inside of the border, which isn't colored.

This is the layerpadding. It's always 3 pixels wide and lies between the
border and the real padding; it appears on any element that has a
'border' attribute, even 'border: none' or 'border: invalidnonsense'. (These
are the elements on which N4 draws a proper block background; without
a 'border' it only draws a background behind the text in the block.)

There is no way to get rid of it but you can make it non-transparent if the
element has 'position: absolute' or 'position: relative', by using the non-
standard properties layer-background, layer-background-color and
layer-background-image. These backgrounds cover the entire block
including layerpadding, even if there is no border. So using a bit of
N4 CSS-hiding magic you can say:

  #thing { position: absolute; top: 0; left: 0; width: 128px; }
  /*/*/ #thing { background-image: url(foo.gif); } /* not N4 */
  /*/*/ /*/ #thing { layer-background-image: url(foo.gif); } /* N4 only */

(which should even validate.)