Please note, IE9 Platform Preview is not a beta release of IE9. The Platform Preview of Internet Explorer 9 will run only in Windows 7, Windows Vista Service Pack 2 (SP2) and Windows Server R2. Microsoft has worked hard and is working hard to bring some new web technologies and standards in Internet Explorer.
Whats new in IE9??
And Many more… So, go ahead and have a test drive.
You can read more about IE9 and platform preview program here