You will notice this blog site will not overflow in the x-direction no matter what resolution you view this site in (I tried upto 640×480). When you have a div area and you are using PRE or XMP to view formatted contents (like I do in this page to view code) within that div — this would be almost impossible to do. Here’s the reason: unless otherwise stated a PRE or an XMP is displayed as is. Take a look at this page for instance. See how it overflows? If you had a shorter viewing area the overflow would be even greater.
The solution is to explicitly say to allow word breaks. Take a look at this page. It does not overflow anymore (assuming you are using IE).
View the code to see the difference.