I decided to work outward & changed the "overflow: auto" to "overflow: visible;" in the "nav" portion of the CSS. That did the trick. I had the chance to check things on IE 6 & everything looks much better now.
One final question. In IE 6, I notice that there is a thin white line appearing beneath each button of the menu & a thin black line appearing beneath each button on the fly-out menu. Do you have any suggestions as to which bits I need to tweak in the menu CSS for IE 6? (I tried fixing these when I first started trying to correct the IE 6 problem & wound up with a right mess on my hands.)