Just Found this,
heise Security – News – Fooling Cisco’s NAC network access control
Security experts at the Black Hat conference in Amsterdam have demonstrated how Cisco’s NAC network access control can be fooled. In a live demonstration using a modified Trust Agent, Michael Thumann and Dror-John Röcher from ERNW were able to gain full access to an NAC protected network using a computer which did not comply with network policies.
Although it was obvious that hackers would target the the Trust Agent, it’s interesting to read a sucess story.