asterisk users - Nov 2003 - Asterisk and Proxy issues

I'm trying to have the following small architecture:

                      PSTN
                        |
        Linux box with an public IP and Asterisk
                        |
                    Internet
                        |
                Firewall/NAT/Router
                        |
	            SIP Proxy
                        |
        IP Phones (or soft phone like X-Lite)

Firt of all, can I do such a schema ? Let assume that the previous
answer is yes... So if anybody that succeed in such a thing can hel me a
bit I would really appreciate... 

By the way, I can put the sip proxy on the firewall or forward some
ports. And I'd like to register on asterisk... 

Thanks a lot for your help,

	chris
-- 
Christophe Sauthier <christophe.sauthier@eikonex.net>
Eikonex - Open Source Engineering  (http://www.eikonex.net)