Internet Explorer 9 'platform preview' available for download (Vista/7 Only)
 

Microsoft intends to update the platform preview every eight weeks. When feedback indicates that things are up to snuff, a beta version of Internet Explorer 9 will be released. Anyone interested in running the preview will need Windows 7 or Vista. Windows XP has apparently been excluded because the preview relies on "advancements in the display driver model introduced first in Windows Vista." The preview is a 32-bit affair, but Microsoft says it should run on 64-bit versions of Windows without issue.

http://techreport.com/discussions.x/18625