Ars Technica reports that it looks like that the final version of Internet Explorer 9 will require Windows 7 users to install SP1

Windows XP users are unable to install Internet Explorer 9, and now it looks like Windows 7 RTM users won't be able to either, at least once the final version hits the 'Net. When Microsoft releases Internet Explorer 9, Windows 7 users will need to have Service Pack 1 before they can install it, according to the Internet Explorer 9 Beta FAQ for IT Professionals.

  Internet Explorer 9 to require Windows 7 users to install SP1