Here is a white paper from Microsoft that describes IPsec and NAP.
Network Access Protection (NAP) is a platform for Microsoft® Windows Server® 2008 (now in beta testing), Windows Vista™, and Windows® XP Service Pack 3 (which includes the NAP Client for Windows XP, now in beta testing), that provides policy enforcement components to help ensure that computers connecting to or communicating on a network meet administrator-defined requirements for system health. Internet Protocol security (IPsec) is a set of Internet Engineering Task Force (IETF) standards that provides cryptographic protection for IP-based traffic. This document provides an overview of the Network Access Protection platform and IPsec and how IPsec enforcement in the Network Access Protection platform works to provide system health policy enforcement for IPsec-protected communication.
I have not read this one yet but, seemed like it would be worth sharing.
[tags]NAP, NAC, IPsec, Access Protection[/tags]