Here are some handy links for folks who have been having trouble with Cisco VPN on Ubuntu.
For detailed instructions click here.
Some concise instructions here.
The VPN Client can be found here.
The patch can be found here.
I have tried the vpnc route and wasn't very pleased, so I decided to go with the proprietary client. However it didn't seem to be a very smooth ride... Anyway I hope that this helps. I will post in detail about this later.
Update: I found this tool which looks promising - Shrewsoft VPN client
It can be found using Add/Remove Applications (Jaunty and earlier) or the Ubuntu Software Center (Karmic Koala).