The body tag on this forum has style parameters set making this forum on the left, it needs to change the style parameter on the body tag (or use CSS instead) to style="margin: 0 auto;" and it will center the forum, but the background is also not centered so they need to center that as well. Background image is doc_bg.jpg so did a search on the source and shows.

html {
background: url("images/fourteenb/doc_bg.jpg") repeat-y scroll 0 0 #95948F;


}

instead of assigning background image to the html css tag, would of made a separate container with background setting margin also to 0 auto;

At least that's what i found out