Getting public IP address of NAT firewall

[Rasjid Wilcox]

Suppose that I have a hardware fireall that does NAT and it is given a 
dynamic IP address by the ISP.  Is there any way for a user of a workstation 
behind the firewall to find out the public IP address of the firewall without 
logging into the firewall?

What I'm thinking is, is there any information kept in the TCP/IP headers 
that would allow me to do this, or is that all lost during the NAT/IP 
masquarade process?

Rasjid.