The Web Standards Project have a page called Acid3 that checks how well a web browser follows certain web standards, especially relating to the Document Object Model and JavaScript.
IE8 only got a score of 20/100. It is a disgrace that Microsoft should release a product that independent tests prove does not work.
Your using Vista, I think?
Go to
Control panel - Programs and Features
on the left hand panel under 'Tasks' click on 'Installed Updates'
Look down the list until you find IE8 and uninstall from there.
very Simple tryt o uninstall IE 8 from Control Panel, Add remove Windows Components. After removing IE 8 your system will automatically be back to IE7.