I had the pleasure of testing this during the alpha stages and had a hard time finding bugs in the product, which is a good thing. If you are using Forefront Client Security and Server 2008, and want to integrate NAP functionality with FCS, look into the integration kit here.
This Solution Accelerator is a collection of software components and guidance that you can use to configure a compliance health policy for computers that run Forefront Client Security. Network administrators can use this Accelerator to assess the health of these computers before they are granted network access. If a computer is not compliant with the health policy for Forefront Client Security, it can be isolated to a restricted network until it is properly remediated. These capabilities are enabled by the new NAP feature in Windows Server 2008.