I probably won’t be adding any more column to the pages. As it stands now, even with just 2 columns (the content and the sidebar) the width of the content area is already quite small. Adding another column will just crowd the page (unless the width of the sidebar is downsized), and making the content area even smaller.
I wouldn’t recommend using table for layout. For semantic markup purposes, use table only for tabulated data, such as a timetable or a list of items in a shopping cart. Use floating divs instead.