Since this is a fairly major issue for a number of people that are running Windows Media Services 2008, I thought this warranted it's own post.  I prevously described the issue at http://blogs.msdn.com/randomnumber/archive/2008/09/05/wmp-unable-to-connect-to-wms-9-5-wms-returning-503-service-unavailable.aspx where WMS returns a 503 error when the server is behind a NAT.  A fix is now published at http://support.microsoft.com/kb/960372.  It also contains two other fixes that were not included in WMS 2008 that had been fixed for WMS 9.