Microsoft released IE8 during Mix 2009. Microsoft spent a lot of time making IE8 comply with the browser standards. When you upgrade your browser to IE8 if you find the web site does not render right. Do not worry there is a simple fix for this.
There is a tag you can place in the Head section of your webpage which will force IE8 into IE7 compatibility mode.
For more info on IE8 compatibility read this article
Hope this helps