I just pulled the site up in IE6 and it looks roughly the same as it did in Firefox. There are just two problems remaining: the difference in color between the background and the gray sections around the rounded corners. Also, the recycling image (people.gif) is displaying about a quarter inch below where it should be.
I recommend keeping position:relative; but dropping the float:right; from the style declaration. Instead, use top: and margin-left: to position it where you want it. This will makes sure it always displays in the correct location.
One other thing that might help: You have both #intro and #introicon set to the same z-index. Because you want #introicon to always display on top, you should set each div’s z-index separately. #introicon should have a higher z-index than #intro.