Background Img's like vb.org

[+buG]

I would like to create images that radiate from the edges of my forum body, like the gradient around vBulletin.org's forum (noticeable under the "Fixed" version). Would anyone mind pointing me in the right direction?

Edit: I made it work by creating an image body equal to the width of my forum body inside photoshop, and added an addition 125px to each side for a "glow effect". I commanded the style var to center my background image and it looks ok. Still, if there's an easier way to do this I would really like to hear about it. Otherwise, disregard.

Thank you!