I have good news for you. You do NOT need the Cisco client on Snow Leopard! It is now built into the OS and I use it everyday to connect to my work VPN.
Go to System Preferences, Network and add a new VPN of type Cisco and give it a name of your choice.
Then, enter the server address. In my case it is vpn1.mycompany.com. Also enter your account name (this is your user name). I left the password field empty since we have an RSA token and it changes every few minutes. If your password always stays the same, put it in.
Then this is where it gets interesting. Go to Authentication Settings. You have to enter the "Shared Secret". You can find it in your Cisco client configuration file (which is plain text). The only problem is that it is encrypted. To decrypt it, simply go to Cisco vpnclient password decoder and paste your encrypted shared secret. Once you have the decrypted string, just paste it. You also need to enter the Group Name which can also be found in the Cisco config file.
That's it! You can now connect to your VPN without the crappy Cisco client!