Adjusting centre column width

I'm using spreadfirefox as my theme and have customised it a lot to, but when I view some pages at 800x600 in IE the centre column is pushed down below the sidebars, such as http://westburygp.co.uk/welcome and http://westburygp.co.uk/eastleigh

I can't see what's pushing these tables down, so any suggestions on what's the culprit?