This is DIV One.
This is typically the header of the page.
This is DIV Two.
This is the left sidebar.
This is the right sidebar. The key issue with absolute positioning—these boxes are out of the flow, so other boxes can occasionally overlap positions.
This is DIV Three.
I have added 151px left and right margins to DIV 3. This opens up space for the sidebars. I have also added position:relative to this DIV, so that it will establish a positioning context—that will allow me to absolutely position the left and right sidebars. Notice that the page background shows through where we cleared the space, since the margins are not part of DIV 3.
This is DIV Five.
This would typically be the footer of the page.
If the footer will be as wide as the window (i.e., not have margins like DIV 3), then you have to make sure that DIV 3 is long enough to clear the bottom of both sidebars. Since the sidebars are absolutely positioned, they are not in the flow -- the only thing that pushes the starting location of the footer downward is DIV 3 in the center.