Here are some other good IPSec links:
www.microsoft.com/windowsserver2003/technologies/networking/ipsec/default.mspx
www.ietf.org/ids.by.wg/ipsec.html
www.unixwiz.net/temptips/iguide-ipsec.html
www.cisco.com/en/US/tech/tk583/tk372/tsd_technology_support_protocol_home.html
http://ipsec-tools.sourceforge.net
http://secunia.com/search/?search=IPSec
www.tcpipguide.com/free/t_IPSecurityIPSecProtocols.htm