Beta 2 for Internet Explorer 7 has been released today. As usual, you can download following the links at http://www.microsoft.com/ie. If you're already running the Beta 2 Preview, you'll need to uninstall that version before you can install the Beta 2 version.
This beta is available for Windows XP (with Service Pack 2) and Windows Server 2003 (64-bit editions or 32-bit editions with Service Pack). Windows Vista will also include IE7 and the Beta 2 for it should be available before the end of this quarter.