It seems Microsoft has updated the public beta of Internet Explorer 7 today. Build 5346.5 is available to anyone, and these versions of Windows are supported in this release.
Internet Explorer 7 Beta 2 for Windows XP Service Pack 2 (SP2) Internet Explorer 7 Beta 2 for Windows XP Professional x64 Edition and Windows Server 2003 x64 Edition Internet Explorer 7 Beta 2 for Windows Server 2003 Service Pack 1 SP1 Internet Explorer 7 Beta 2 for Windows Server 2003 ia64 Edition (Windows Server 2003 for Itanium-based systems) Download IE 7 Beta 2