If your firewall is blocking the online registration of KMS (Key Management Service) for Vista/Server 2008, then you need to activate it offline by calling.  The US Number is 1-866-740-1256, but there's a trick:  The IVR system will ask for your Installation ID in "groups", but in Server 2003's KMS console (slmgr.vbs) you are given one long string.  If you don't pause at the right time, the IVR will get hung up and tell you "please only give me the group X".  The grouping magic number is six, so just stop between saying each six numbers, and imagine the dash between them :).