I had the same problem on my site (shameless plug).
I had the nav section "float: right" and the main body of the page has a background image about 250px across aligned to the right and "repeat-y". I then added something with "clear: both" to it. Here is the W3Schools and the CSS clear property.
I placed the clear at the bottom of the "page" classed div. My page source looks something like this.
body
-> header (big blue banner)
-> headerNav (green bar at the top)
-> breadcrumbs (invisible at the moment)
-> page
-> navigation (floats to the right)
-> content (main content)
-> clear (the quote at the bottom)
-> footerNav (the green bar at the bottom)
-> clear (empty but still does something)
-> footer (blue thing at the bottom)
I hope that helps :)