Bill,
It appears you have several problems which may have all eminated from the rounded box code.
The featured products area shows blank space at both the top and bottom of the white area alloted for these products as do the boxes inside this showing each product.
Check your rounded box code against the original for any extra <p>, </p> or even   tags. One of the easiest ways to crash test this is to comment out one tag at a time until you find the one causing the problem.
I remember seeing this error a while ago when I used this code but can't remember which line it was I changed to fix it. However because it's only in your featured products section there is little need for you to crash test the menu files that make up the left and right side boxes.
The extentsion beyond the right of screen is only an issue in IE, Firefox shows the rounded corners of the right hand boxes so without getting too deep into it I would suggest looking at your CSS first and seeing if your borders are too wide.