ARS Technica notes Microsoft has changed its position regarding IE9 on the Windows 7 operating system: Service Pack 1 will not be required to run the browser. The new browser will require some patches that are part of SP1, but these updates will be made available separately.
Microsoft has now changed its public position: Service Pack 1 won't be required to run the new browser.
When Microsoft releases Internet Explorer 9, will it require Windows 7 Service Pack 1?
No. Internet Explorer 9 will install on systems that have either Windows 7 RTM or Windows 7 with Service Pack 1 (SP1) installed.
Internet Explorer 9 will require a number of patches before it can run; Microsoft has made many fixes to the Direct2D and Media Foundation APIs that the new browser heavily depends on. These fixes will be incorporated into Service Pack 1. However, standalone updates are also available, and the browser will install these if necessary.