Our theme demo http://demo.hotjoomlatemplates.com/wordpress/cosmetics/ works fine on IE9 and it also validates HTML code here: http://validator.w3.org/
I don’t know what modifications your did, but your site has many errors. Check your site here: http://validator.w3.org/
You must develop your site according to HTML/CSS rules if you want to keep compatibility in all browsers, especially in older browsers.
Regards
Milos
