How can I share a Cisco VPN connection?
I don't know if this option was also available in Snow Leopard, but if you are on Lion you could try the following:


Set up the native cisco client - if you don't know how, you can use this handy guide I created a few days back
Once you have tried and confirmed that everything works, your VPN connection should show up as one of the options in the Internet Sharing part of Preferences Sharing.
select the connection, choose on which network connection you'd like to share it and you're done.