i've been playing with your page for the last little bit... here are some observations fwiw:
Your css is confusing, partly because it jumps from pt's to px's when referring to sizes, padding, margins, font ect... Just for what it is worth, you may want to consider going through it and adjusting those... as in stick with one or the other... everybody has their tendencies, but for reasons.. many, me included use pt's when referring to font size and line height, and px's when talking about margins, padding ect.. mixing the two as is in the css's your using, is asking for a premature bald head...
You have listed several places things like margin: 1px 0, this is fine, but if you want to maximize your cross browser use you may want to go back and add the other two, such as margin: 1px 0px 0px 3px;
If you are going to link to two or more external css files, you may want to consider only setting a wild card '*' once, same as with the body, HTML, ect.. it can trip out browsers--- it has been said css is like a private in the army, it does exactly what it was last told to do.. but IE knows nothing of discipline, and will do some crazy stuff when it is being told to do several differing things for the same tag- in different places.. it can be unpredictable.
IE also doesn't play nice with negative declarations.. So you need to work around those margin: -10px; and such.
The killer for that .white_box, I can't remember which place, but you have the declarations top:, and left: assigned, that is fine but it is not a absolute positioned item, which-- guess? trips browsers out, especially aging and senile IE.
Final shot: you have declared in several places things like position:relative; ... just another for what its worth thing, but it is relative by default in every browser I know of, believe it or not IE too! It's been my experience you should only declare what you want to change, not what is provided my default.. It confuses the issue for later adjustments, and also for some hapless browsers (uhem, Mr, Gates)...
I highly rec you use FF or Opera for development- prefer FF w/ the devel plug-ins.. not for just what you are thinking either, but 'cuz it is compliant.. It is also stricter.. Your always going to do the IE reacharound, but if it is close to compliant in the start, it is easier to find problems later..
you got a laundry list man, best of luck!