I just found out about ie7-js ;
IE7 is a JavaScript library to make Microsoft Internet Explorer behave like a standards-compliant browser. It fixes many HTML and CSS issues and makes transparent PNG work correctly under IE5 and IE6.
http://code.google.com/p/ie7-js/
It looks like it's really good, but is it really working (the current issue list looks quite scary)? Have you already worked using this with success?
Another question is how slow the script will make the website in IE ?