Cisco VPN client with NAT

Hello everybody
We have Cisco router 805 with NAT. So we have one official IP address and 10 internat IP addresses. We need to connect to our partner using Cisco VPN client (I’m using version 4.0.3.D) I cannot connect to VPN server when behind router. Using dial-up it works just fine. Any help would be much appreciated.
Thank you
Jaro Griscik