Can you tell us exactly which links are causing problems? I'm not seeing any difference between IE 8 & FF 3.6.
The real issue as I see it is that you are using a whole lot of absolutely positioned divs (layers) which don't work well if the visitor isn't using default font settings. Plus you are using h4 for body text instead of paragraphs, very bad from an SEO & semantic html point of view.
The menu you are using won't work for visitors using IE 6 so I'd suggest using the Project Seven menu which does. Tutorial at
http://by-expression.com/post/2009/09/22/CSS-Based-Dropdown-Menus.aspx Then the page would look more like
http://wizerways.net/rgs/ (note I removed the slideshow and stat counter for the purposes of demonstration) I wasn't sure which of the javascript files and the exe link were supposed to run the slideshow (though exes are not a good idea) when I substituted the Project Seven menu for what you were using.
On a couple of side notes you shouldn't have the browser resize your graphics. They typically do a very bad job of it and don't use spaces in file or folder names (that's what the %20 means) because if the encoding fails the link will break.
I also made the content area slightly smaller so that there would be a border of the darker green in a 1024px wide browser window instead of a horizontal scroll as there is with 1000px.