First! maybe move the .shoutbox class to the bottom of the page.
Now! Change your body style around line 11 in your style.css to this..
Code:
body{margin:0px 0; padding:0; color:#000; line-height:1.4em; font-style:normal; font-variant:normal; font-weight:normal; font-size:74%; font-family:Arial,Sans-Serif; color:#FFFFFF}
Then follow what Fynnon said in regards to what you want the body's backround colour to be.
If that isn't the correct image it might be .content but it's probably the body image.