I tried your suggestion but didn't get very far. I've now altered the margin settings and the page works in IE however this change now means that in FF the main box overlaps the left column.
Whats the best way around this? Is there a way i get set different margin values for different browser types or is there a little tweak that works in both?
Can't get through to your tiny.cc link, but there shouldn't be any need to alter margins for different browsers. The reason I suggested display:inline; was because IE doubles the margins on floated elements that do not have that property. This is still sounding like a common box model bug to me. I'll try the link again later on and get back to you.
Your div#main is overlapping your #sidebar in FF as you have set div#main to position: absolute taking it out of the document flow but haven't positioned it with any co-ordinates. Therefore it's in it's default position in relation to it's containing div (#wrapper) which is top left or 0 0.
Your declaration for #main should read:
#main { position: absolute; left: 206px; /*This is just an example figure which would give you a 20px margin on the left */ margin-left: 10px; margin-top: 10px; float: right; }