Internet Explorer has been a PitA for a lot of web developers. It just is not standard’s complaint and they don’t try to be. Even in IE7 you would think they would provide a more standards compliant browser, but no, then don’t seem to. Read these two articles, IE 7.0 Technical Changes Leave Web Developers, Users in the Lurch and Microsoft Drops The Ball on Internet Explorer 7 Standards Compliance.
Also checkout http://www.ie7.com. Kudos to Firefox, not sure if they registered the site or some user, but either way its interesting advertisement. As you would have noticed I am having problems with IE 7 for my site, hence I am supporting only standards compliant browsers, Firefox and Opera. NoIE.