I made a few tweaks to the CSS, and it now seems to be working in Internet Explorer (at least for version 7). The functionality isn't quite the same but at least the nav bar is usable now. I'd be grateful if IE users could mention if anything is amiss.
I also met my first GameDev.net member face to face today, when I had lunch today with "Avatar God". I can vouch that he's still alive and well. Tomorrow he'll be heading over to Melbourne for a few days if anyone wants to keep an eye out for him.