In difference to FreeS/WAN, in IPsec of 2.5.x the IKE daemon "racoon" (taken from KAME) is used instead of "pluto" of FreeS/WAN. It has a different configuration syntax than "pluto", note also that the IPsec setup is splitted into 2 parts (IKE and topology setup). Until some documentation is filled here, take a look at Linux Advanced Routing & Traffic Control HOWTO / IPSEC.