ipsec --version will tell you the version of Openswan (and kernel module, if applicable) installed.
Good examples:
Linux Openswan U2.1.4/K2.6.6-1.435.2.3 (native)
This example shows Openswan Userland 2.1.4 installed, using the 26sec stack, on kernel 2.6.6-1.435.2.3 (Fedora Core 2)
Bad/broken:
Linux Openswan U2.1.4/Ksuper-freeswan-1.99.8
This example shows Openswan Userland 2.1.4 installed, but a Super FreeS/WAN 1.99.8 kernel module (ipsec.o). This will not work, and you will get errors like:
ipsec_setup: /usr/libexec/ipsec/eroute: pfkey write failed, returning -1 with errno=22
