The best that I can tell it will be supported as long as Windows Vista, since it is included with Vista. I am not sure if it is included with Window 2008 Server or not. I know it comes with Windows 2003 server still and will be supported as long as Windows 2003 server is.
Good for MS I think. As the users who dont upgrade to ASP.NET are transfering to PHP. I personally will be moving the rest of my classic ASP apps to PHP as I'm finding it easier and cheaper to transfer.