All Windows 7 users are free to play around with beta version of Internet Explorer 9 for now, but the final version will require an update to service pack 1.
Microsoft confirmed the requirement on its FAQ for IT professionals. This is not a major roadblock for consumers, who shouldn't have much trouble upgrading on their own. But in the enterprise, IT departments will have to deploy the service pack to their users before putting IE9 in place -- a more daunting task.
Perhaps that's why a Microsoft blog post from earlier this week encouraged businesses to install Windows 7 with Internet Explorer 8, and fast. It's possible that Microsoft doesn't want enterprise users mucking around with the IE9 beta, only to be locked out of the final version. That would put IT professionals in a difficult position of needing to deploy the service pack in short order.
More likely, as Ars Technica points out, Microsoft doesn't want businesses who are still using Windows XP and Internet Explorer 6 to hold off on upgrading until Internet Explorer 9 is ready. The company is effectively telling businesses to please hurry up and install Windows 7 and IE8, to avoid the hassle of moving straight to service pack 1 and IE9.
Rich Reynolds, Microsoft's general manager for Windows Commercial Product Marketing, assured that the high compatibility between IE8 and IE9 will make upgrading easier when the latest version of Microsoft's browser is fully-baked.
Neither IE9 nor the first Windows 7 service pack have release dates, but the public beta of service pack 1, which became available in July, expires in June 2010.