The upper table cells will be the tabs. Give the active tab the color of the content table cell's background so they look like they are one and give the other "tab" cells a different color with a line border on the bottom. Make sure the table cells also have side borders so they look separate.
Just a possible example, I know that there are other ways of doing this:
You could also make images to represent each of the tabs...two images per tab, one being the 'selected' tab image, the other the 'unselected' image, and run them in a table across the top of the screen, each one also being a link of course. When the right page is chosen, the 'selected' tab image for that page is used, the rest use the 'unselected' image.
Take this suggestion with a grain of salt...I'm not an accomplished visual web designer....Arbitrator's suggestion is likely the better option.