Did you run the CEICW [email and internet connection wizard]? When you have 2 NICs in stalled in a SBS 2003, this configures your external NIC to block ping for security.
Are you attempting to use RDP to access your SBS? If you are, do you have port 3389 pointing to your server? Is your server setup to accept remote access?
A none response to a ping request does not mean you are unable to establish a remote connection. It only shows that your server is not responding to the ICMP request.
Tell us more about what procedures you are using from the outside to connect to your server. Are you using another TZ170 or are you trying to use a software VPN client?