Working with iptables (CentOS 5.2) .... "allowing ICMP" and "opening up SSH" ...

Hi:

I have PBX in a Flash 1.4 (runs on CentOS 5.2) ...

The PC this PBX runs on has two NIC cards.  

One NIC is on a 172.x.x.x subnet (NAT) with no access to the Internet from the LAN.
One NIC has a LIVE 'static' IP address which reaches right to the ISP with no router/firewall in front of it.

I am not able to 'ping' the LIVE 'static' IP address the 2nd NIC is assigned.

I've setup PBX in a Flash 1.4 in the past (in a few other configurations), and I've never really been able to get ICMP to work.

I would like to be able to ping the LIVE static IP address from another host on the Internet.  

NOTE:  ICMP replies 'work' if you try to ping the 172.x.x.x IP address from another 172.x.x.x host, but not the LIVE static IP address assigned to the 2nd NIC.

I am thinking this is not a PBX in a Flash 1.4 concern, but rather an iptables configuration.

How (or what) do I configure inside CentOS to 'allow' incoming ICMP to reply?

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Next, if use PuTTY from another PC on the 172.x.x.x subnet, I can SSH into the PBX in a Flash 1.4 PBX.  

If I am on another 'Internet' PC, I cannot SSH into the LIVE static IP address of the PBX in a Flash 1.4 PBX.

Again, I think this is quite possibly a CentOS iptables/firewall boggle.  

How/what can I do to be able to SSH into the PBX in a Flash 1.4 PC from another PC on the Internet?

Thanks in advance for your time and tips.