Another CSS/IE conundrum

What I want to do seems like it should be so simple, but if I had hair, I'd be pulling it out.
I want my page divided into four sections, each of which span the entire width of the page. Sections 1 and 2 are fixed height. Sections 3 and 4 shared the remainder of the page 50/50.
The following example (online here) works perfectly in Gecko-based browsers, but not in IE.

Apparently, IE doesn't "do" the bottom CSS attribute. Playing with the DOCTYPE to switch the browser into and out of standards-compliant mode doesn't seem to have any effect.
So without resorting to tables (which introduce nastiness of their own when I start populating the sections with their intended content), is there a way to accomplish this using CSS? I've run outa ideas!
bear

seems to do the trick in IE6 and FB (90.4% fills FB exactly, but still not quite in IE)

Bear,
I will play around with this when I get time. I am hung up at work trying to not be here all night every night next week for a deadline.
Eric