If you are using the Cisco VPN Client on Vista (if you can even get it installed, you need one of the latest versions) Then you probably have ran into connection issues. "Connection Reset By Peer" or "Failed to Enable Virtual Adapter" or "User Authentication Failed" etc etc. I recently redid my Vista box and was just having major issues with the Cisco VPN Client. It would connect for 3 minutes, disconnect. 8 minutes, disconnect. 2 Hours, disconnect. I couldn’t stay connected for any period of time. A possible fix?
Set up a constant ping. To a server or device on the network you are connecting to. I have been connected non-stop for 2-3 days now without issue. This was just not happening before.
start->run->cmd> ping <ip or server name> -t
and just let it run in the background, it seems to keep the VPN Client connected!