I like it! Very readable and cross-browser usable, and good use of whitespace. The best designs have a simple and functional aesthetic, in my opinion.
Personally I would ditch all of the Dreamweaver scripts and use CSS for your rollovers (you can preload images with CSS easily just by placing them at the end of the page with display:none). And I would change the structure of your menu link code a bit to make it work for text/cell phone browsers and be a bit more semantic. Consider using a <ul> list instead of just loose links, and make sure that the text for those links is in there somewhere (if you don’t want to use link title tags so as not to interfere with your snazzy tooltip script, make sure that the images have alt tags).
Another thing you might consider is using absolute positions for your divs so that you can bump the content up towards the top of the page (which improves search engine rankings a little). I think you could probably do that pretty easily with this layout. I usually end up floating everything myself, but a little voice in the back of my head always tells me I’m being lazy.
