Weird gaps in IE

I’m having a really strange issue with this site I’m working on, and can’t seem to find the source of the problem.
I have a pretty basic site here with a div based navigation to the left (<li><ul>stuff etc.), and an iframe with the body content on the right, but there’s a really strange thing going on in internet explorer. I’m getting a gap between the navigation and the body background image. This means the iframe is shifting over 150 pixels. (on a PC it also seems to shift 150 pixels down).

Here’s the thing, it looks absolutely perfect in Firefox. In Safari, it starts with the 150px gap to the right, but once a link is clicked, the gap goes away. I’m guessing it’s something with the navigation, but it looks to be put together properly.

http://www.raincommunications.com/2005/raintd2.html

the stylesheet is right here::
http://www.raincommunications.com/2005/rainstyle.css

let me know if your eye spies anything fishy, or if you’ve had a similar problem. it’d me much appreciated, since my brain is about to explode.

cheers,
Dave