What browser are you using? Presumably some version of IE since this is caused by your browser having a bugged box model. If you're using IE6 try upgrading to IE7, it supposedly has much better (although still flawed) standards support.
Or just use any recent version of Firefox/Opera/non-IE browser which will almost certainly work correctly by using scrollbars within the code/quote box instead of requiring horizontal scolling of the entire window and messing up the whole layout.
This definitely shouldn't be "solved" with a fixed width value. Not good design karma.
