Tom,
I have looked at OpenVPN but for some reason i'm having issues with generating certificates using their howto and i used the rpm from Dag. While i continue my fight with this is there any other options out there?
I replied to your issue on the OpenVPN mailing list, it is the way you are setting your environment.
When running behind the NAT firewall, you will need a rule in the firewall to forward the inbound connection to the VPN. Once the connection is established, all traffic will pass thru the NAT/Firewall over this connection.
I am running the setup you are describing, using Windows and both Fedora and CentOS and it is rock solid.
Brett