It's pretty simple. I hope you don't expect we will design it for you. But it two words you need to create an additional containter let's call it middle with background image attached to it this will create left and right gradient effect.
the way i did it on my site was to make one background image that's really wide but short vertically. it's over here. (oops, forgot about my anti-hotlinking .htaccess.) it handles body background color, gradient edge. nav column color, content column color, right gradient edge and background color again.
then in the css i appled it to the BODY of the page, centered, starting at the top, and repeating only in the Y axis.
then i put the page content in a div that gets centered over the areas it's supposed to be in, and made the columns fit into the appropriate spaces over the background image areas.
Set up one centred wrapper div using margins left & right : auto & set the width you'd like then give it a background image (which is the slice with your gradients etc - only needs to be 1px high if you like) and repeat it in the y-axis. For example;