Drop Shadow Center Column Website web page

How can I add a drop shadow effect to a website that has one center column?

Some examples of what I mean:

lala.com mint.com

Those are both done with background images:

See Mint: http://www.mint.com/images/global/body.jpg
See LaLa: http://s.pplala.com/static/24.4.1-25/images/background.png

LaLa's is repeating, where Mint uses one large image.

They've done it with a centered background-image on their body. The image has the shadow on it.

If you're ready to sacrifice a little beauty on older browsers, I would suggest you use -webkit-box-shadow and -moz-box-shadow. Coding designs that degrade gracefully encourages people to use recent browsers for a better Web, while not making your website unusable for people who can't.