I like the general look of the site although I think it is a little top heavy and would benifit from being more vertically central or even just moved down slightly from the top of the page.
In terms of the functionality it appears to work well in the standard javascript enabled browser however I would be concerned about the use of javascript for critical website functionality. Perhaps you should investigate how the site would appear if the user did not have javascript enabled etc. One very good alternative to use is a purely CSS driven menu. That way you can write it so that even text only browsers are able to view the site and navigate sucessfully.
If you are aiming for good accessability test the site in all main browsers: IE, Opera, Netscape, Mozilla using various versions and consider people using Linux (Konquer) and Mac browsers.
Good luck with the site 🙂
