I'm using DW CS4 and am using the 2 column fixed left sidebar with header and footer.
I want to make sure the main content div is never shorter than the length of the sidebar. I've got a coloured background, but want the bottom of the sidebar and main content div to be the same, if that makes sense?
For equal height columns, create a 2-colored background image and repeat-y (vertically). This technique is called Faux Columns. See examples below.
3-Col Layout Before -
3-Col Layout After -