So Microsoft does make it more complicated than it should be. What a shock!
Anyway, I was confused because NAT stands for network address translation, which simply means that the router translates connections from your "internal" network address, usually 192.168.x.x, into the "external" IP address given to your DSL/cable modem for transmission over the Internet.
Port forwarding forwards incoming data packets to specific machines on your "internal" (LAN) network for particular applications and really has nothing to do with NAT other than knowing which LAN IP address to forward to. For example, if you have a web server on your LAN, any incoming packet labeled with port 80 should be forwarded to that server.
The link to the Apple discussion gives good info.
Steve