This layout is fluid with respect to the yellow stuff in the center. Left and right boxes always will be visible. All the three colums use a background color, i.e. contents will be visible even if the page will shrink a lot. This is a fairly good layout, given its simplicity. Of course, this design needs some tuning. E.g. adding so-called "tube" divs within the three column boxes, changing colors, etc.
Some fake content.... Some fake content.... Some fake content.... Some fake content.... Some fake content.... Some fake content....
Boxed item A
Boxed item B
Actually quite a somewhat longer boxed item C