Latest versions of:
CTA is 2.01. There is a limited availability release 2.1.18.0 however only available for NAC 2.1 beta participants.
http://www.cisco.com/cgi-bin/tablebuild.pl/cta
ACS is version 4.1 for Windows
ACS images are now posted on CCO:
http://www.cisco.com/cgi-bin/tablebuild.pl/acs_gemini
ACS evals: http://www.cisco.com/cgi-bin/tablebuild.pl/acs-win-eval
Other forms (Unix and Appliance version):
Cisco Secure Access Control Server for Unix (CSACSU), Version 2.3.6
Cisco Secure Access Control Server Solution Engine (CSACSSE), Version 4.1
CSA is version 5.1.069
http://www.cisco.com/cgi-bin/tablebuild.pl/csa
Note 5.2 is coming out soon.
BTW if looking at a NAC solution I would highly recommend looking at our NAC Appliance solution. It is truly the most flexible, turn-key, and widely deployed NAC solution in the market. www.cisco.com/go/cca
