Please see Cisco's response here for possible work-arounds.
Cisco NAC Appliance (formerly Cisco Clean Access) is an easily deployed Network Admission Control (NAC) product that uses the network infrastructure to enforce security policy compliance on all devices seeking to access network computing resources. With NAC Appliance, network administrators can authenticate, authorize, evaluate, and remediate wired, wireless, and remote users and their machines prior to network access. It identifies whether networked devices such as laptops, IP phones, or game consoles are compliant with your network's security policies and repairs any vulnerabilities before permitting access to the network.
All current (<= 188.8.131.52 at the time of the release)
2006-08-20 (vendor), 2006-08-25 (public)
Related previous reports:
Andreas Gal (http://www.andreasgal.com/)
Joachim Feise (http://www.feise.com/)
The registry settings to masquerade the Windows TCP/IP stack were derived from sec_cloak written by Craig Heffner.