1. Install the vpnc service and GUI components via a Terminal
sudo apt-get install vpnc network-manager-vpnc network-manager-vpnc-gnome
2. Use the Network Connections Applet to create a new VPN Profile.
You may also import pcf files from a previous Cisco IPSec client install on Windows/MAC OS.
The Gateway is the hostname/IP address of your headend
The Group name is the tunnel-group/crypto isakmp client group configured on the Cisco Headend.
The Group password is the password associated with the Group.
In the Optional Section enter your username, and Domain if needed. This may require trial and error.
Encryption Method/ NAT traversal, I would try defaults...but if they don't work some trial and error might also be necessary
3. Use the Gnome Notification Area Network Management Icon to select and connect to the VPN. Also use the same section to disconnect when done.