I've read and re-read the tips on Craig's website and have been able to
browse the web ONLY when I have NBM set with public and private IPs. My
server (NW 6 SP5) has two network cards now. As I understand things, for
proxy (authentication is disabled) to function in this type setup, I only
need one NIC and no NAT configured.

Simple diagram of *desired* configuration follows: LAN -> NBM Proxy ->
Firewall (running NAT) -> router -> ISP.

The only configuration I can get to "work" is: LAN -> NBM Proxy -> router
-> ISP