Not bad, forum logo area breaks apart in Firefox though.
Remember that transparent .png images don't look the same in Firefox and IE, so... your search/memberlist/calendar/help icons all work fine in Firefox, yet have a darker square box behind them in IE.
IE User here, and yeah the header has a few problems with it, first there's a square grey box behind the top images, and secondly the side lines on the outer edge of the forum don't go through the header.