I changed the right and left images that are used for the hover state from PNGs to GIFs. This solved the bad display problem for the main menu line in IE6.
I am still having a problem with the drop-down menu under "galleries" in IE6. Although I have set the width property for the sub-menu items, in IE6 the sub-menu appears as if it is displaying the full width of the div and then blinks down to the preset size as you mouse up and down the sub-menu items. Is there a way I can fix this?