There is a great article on the NAP team's blog on just how update enforcement works in NAP. 

"The easiest way to discuss update enforcement is to step through each part of the “Security Update Protection” section of the WSHV user interface. This is the dialog that appears within the Network Policy Server (NPS) console on Windows Server 2008"

Regards,
Anthony

Anthony Clendenen | Solutions Engineer | 1E

http://configmgr.com

© Anthony Clendenen