The page (by using java) http://www.auditmypc.com/anonymous-surfing.asp and http://www.auditmypc.com/internal-ip.html can show the external ip address and the internal IP address / private ip address.
Is it possible to show this internal ip address in the example configuration (for Vista) when there is found a internal ip address so this replaces the external ip.
The example configuration for Vista is also working on xp (even after a reboot).
The netsh portproxy still needs to be re-enabled. But that is an other story (and no problem).
The site mentioned uses java to find the private address.
It is also possible to find the internal ip address manual.
start, cmd, ipconfig, use the adapter ip in use.
The reason for automatically replace the external ip by the internal ip is to prevent the use of a not working configuration.
Edit:
A simple program to show (first) local-ip and (second) external ip.
http://www.softpedia.com/get/Network-Tools/IP-Tools/IPaddress.shtml