Interoperating: Check Point VPN-1 or FW-1
AERAsec's Firewall-1 NG site (PSK, X.509, Road Warrior with X.509, other algorithms)
AERAsec's detailed Check Point-Openswan support matrix
Checkpoint.com PDF: Linux as a VPN Client to FW-1 (PSK)
PhoneBoy's Check Point FAQ (on Check Point only, not Openswan)
Check Point NGX to Openswan running on Linksys/OpenWRT (DDNS, QoS, PKI)