Ok, I took a look with IE7 and it looks like the blue background image is shifted to the right too far. In FF it looks OK. In IE6 it is completely messed up. I don't see anything but the menu and the dropdown part is too high and overlays the main level of the menu.
It also looks like there is javascript that we don't have that is part of the menu. There are definitely things missing from here that must be setup in the javascript. I much prefer the CSS menus that don't use any javascript. Stu Nicholls has a nice one that I like. It works a little differently than your current one. You might check it out and its variations out at
www.cssplay.co.uk and see if one of them will work. You have to ask permission to use them.