In IE5, the vertical gap between the boxes varies from page to page, even though the same stylesheet is used throughout.
The gap above should be one pixel.
Netscape 6 and Mozilla 1.x do not exhibit this glitches. However, when a column gets too narrow, NS6 lets the text jut out of the column and overlap the next!
In CSS every object occupies a rectangular space with a border (The one pixel dotted line in this case). Outside the border the box is separated from other objects by a margin. Inside the border is padding that separates the border from the content (e.g. this text).