I have heard several complaints about Cisco VPN client for Linux. It's a kernel module, so it's a mess.
However, few days ago I had to connect to one site using Cisco VPN. I got even Windows client. Which didn't work from emulated Windows on my Linux box... What should I do?
First idea to search Debian packages proved like a right thing to do: I soon found vpnc which had all the tools needed for transition. Even tool to convert Windows Support_template.pcf to format sutable for vpnc!
I also wrote a short tutorial how to install and configure it which might be helpful.