I'm going to recommend my own page on vpnc. The page is aimed mostly at RH based distributions, but the instructions are pretty generic.
It should work with almost all Cisco VPNs.
I have tried Cisco's VPN client, but it was pretty bad--it had trouble with SMP machines, 64 bit machines, and so on. One assumes it's improved since then, but VPNC is, IMHO, as easy to use.
http://home.roadrunner.com/~computertaijutsu/vpnc.html