Introduction
Nearly three years ago, as the IE development team called for developers to clean up their CSS hacks in preparation for the release of IE7, I wrote a blog post called Future-proof your CSS with Conditional Comments, which detailed how to use a proprietary Microsoft technique to avoid CSS hacks by feeding separate CSS (or JavaScript, or whatever) to different versions of Internet Explorer.
http://dev.opera.com/articles/view/supporting-ie-with-conditional-comments/
