Are you using FireFox & the Web tools?

I checked the one box that you have and the item is as follows:

Class = .sideBoxContent
ID.....= #informationContent

I would try finding this:
Code:
.rightBoxContent, .leftBoxContent, .sideBoxContent {
	background-color: #ffffff;
	padding: 0.5em;
        font-size: 1.1em;
	}
and separate the .sideBoxContent to make it look like this or apply to all three.
Code:
 .sideBoxContent {
	background-color: #ffffff;
	padding: 0.5em;
        background-image: url(../images/box_back.gif);
        background-repeat: repeat;
        font-size: 1.1em;
	}

.rightBoxContent, .leftBoxContent {
	background-color: #ffffff;
	padding: 0.5em;
      font-size: 1.1em;
	}
I added the repeat statement...You are calling the same image that you are using for the sidebox headings and it is only 5px by 40px: not a likely candidate for a background fill image. And did not understand how you are thinking that this is akin to the "sliding door" method.