Dinh:
The easiest way to fix it is to put the sidebar before the banner div in the markup (you dont need to change anything else, although I think you might wish set magins and paddings on the body to zero, it works ok).
But you should not have to change the markup to format the layout, so I think the best way to do it is using negative margins.
Anyway the other replys are already explaining it.
Best regards,
Isabel Santos
