In my browser, Firefox on Linux, the #main content is centred and is pushing the #rightcol down. Can’t see from the css, using Firebug, what might be causing this as it appears you want the #main to float left and the #rightcol to float right – appears to be caused by the ‘Open Days’ link in the nav bar above it which drops down probably due to the widths of the three list elements.. Also the containing div, #content?, does not extend down to include the floated #main and #rightcol divs.
Don’t have time to check further.
Mike