Thanks to a tip from Rodney McPhail, I’ve squashed a Mac/IE5 bug that made the menus at the top disappear when you hovered over them.
It seemed that all I needed to do to fix it was place the navigation menu in the header itself vs. positioning it absolutely. Once I fixed the problem, it came to mind that maybe all I had to do was mess with the z-index of the menu, but I’d rather have the XHTML structured this way anyway. I think it’s more logical. So thanks Rod, and let me know about any more bugs you find!