Webpage rendered differently in IIS6 and IIS7

We are using IIS 7 in development environment. All the pages are rendered more or less the same in Firefox and IE8 in IIS 7. But when I deployed to test which runs on IIS6, the pages appear different on IE8 (they work fine on Firefox). They appear dramatically different.

I used IE web dev tool开发者_如何学运维s to see what styles are getting applied, it seems a few styles are overridden differently although the CSS file are exactly the same on both environments. Since the webpages appear fine on IE8 (on IIS 7), I believe its an IIS 6 issue.

Does anyone have any insight on this?