I just noticed the Network Policy Server (NPS) guys are hosting an online Chat on April 10th.  This is a great opportunity to ask the really tough questions on NAP, NPS, IAS, RADIUS, etc.  Be sure to ask about 802.1x switch and router support, IPSEC boundaries, NAC compatibility, and compatibility with other operating systems. 

For detailed information in the chat, see http://blogs.technet.com/nap/archive/2007/04/02/longhorn-web-chat-the-network-access-protection-nap-server.aspx.