Cisco has licensed its Cisco Trust Agent technology to Network Associates, Symantec and Trend Micro so

Currently the Cisco NAC software only works with Cisco network equipment and Microsoft Windows NT, XP and 2000 operating systems.

Without the secret handshake Mac OS, Linux, Solaris and other operating systems will not be able to connect to a Cisco Self-Defending Network which limits its usefullness for ISPs.

Sounds of limited use anyway, the OS that can use it seem to be more usually wormed/virused that the OS than can't (regardless of the add on security products). brandon