Free Internet Explorer debugging tool: Microsoft Expression Web SuperPreview for Windows Internet Explorer
Expression Web SuperPreview for Internet Explorer is a free stand-alone visual debugging tool that makes it faster and easier to migrate your sites from Internet Explorer 6 to Internet Explorer 7 or 8. Expression Web SuperPreview for Internet Explorer shows your web pages rendered in Internet Explorer 6 and either Internet Explorer 7 or Internet Explorer 8, depending on which version you have installed on your machine.
More at the Expression Web team blog