Here are some links to information on how to do the Radius-AD integration:
http://deployingradius.com/documents/configuration/active_directory.html
http://wiki.freeradius.org/FreeRADIUS_Active_Directory_Integration_HOWTO
http://articles.techrepublic.com.com/5100-10878_11-6182945.html (Configure Cisco routers to use Active Directory authentication)
See KB 45690 for information regarding single sign-on. Some customers would like to enable logging onto the Enforce server via Siteminder or Tivoli WebSeal. However, single sign-on for Symantec DLP is currently not supported.