Windows Sharepoint Services (WSS) 3.0 external connection issue

Installed SharePoint (WSS 3.0) on Windows 2003 server, configured ISA server, configured IIS 6, and DNS. I can hit site inside network, but not from outside.

From the outside, I can see the request change from the public URL to internal URL, then fails. Reports back ?Page cannot be displayed?

Please assist if you have any thoughts.