I had the chance to attend Cisco Partner VT event for security this week and they had several sessions on the NAC CAS (Clean Access Solution - now the Cisco NAC Appliance) solution. This is the technology they picked up from Perfigo - not to be confused with their other acquistion of Protego Networks which is now the MARS product.
Cisco seems to really be ahead of almost everyone else in the NAC space in terms of having a product that is easy to implement, is robust and can do all aspects of what you would expect from a NAC Appliance. I think the hardest thing about this market is the lack of a common definition of NAC and what it really mean, but that is to be expected from a new technology.
At this time, points go to Cisco for a complete and quick to deploy solution. I think Microsoft will have some advantage once the install base of Vista becomes significant (2009?) and they are able to have a complete story around AD, IPSec, Federated Domains and running everying on IPv6. Doing something like NAP become much easier once all those items are in place.
I will expect to see more and more announcements come out as the 40+ vendors who are all trying to get mindshare in this space dook it out.