IE Mac odd float characteristics?

I have a site at
http://www.chancesend.com/news.html
which displays fine in all PC browsers, but does an odd thing in IE for
the Mac.

In the div#main section, I have the main #content div (starting with the
News header), and I have the two sidebar divs #joinlist and #subhead.
Normally, they are supposed to be aligned just below the header.
However, IE Mac is displaying the main #content div below the sidebars.
It's readable, but very ugly.

I've tried messing around with the float and clear parameters in order
to fix the problem, but I have been unsuccessful so far (coupled with
the fact that I don't have easy access to a Mac). Can anyone give any
insights?

-Ryan