This looks like it's a case of the IE6 1px jog which can be solved by a few different fixes.
You will only want to apply these fixes to IE6, using your favourite method (conditional comments, star html hack, whatever). You could
apply background position to #container_bottom
container_bottom { background-position:1px 0; }
apply a left margin or padding to #container_bottom
container_bottom { margin-left:1px; }
or float #container_bottom to the left and give it a width
container_bottom { float:left; width:800px; }
Any of those seemed to work for me.