It should ask you which IP address you want to forward the port to. It should be the same as the local IP address of the server you are using. To find out your local IP address, click Start, then Run, type "cmd" and press enter. Once in command prompt, type "ipconfig /all" and press enter. Look for "IP Address:" which should be followed by a local IP address, and it should start with 192.168.. or .. actually there is another IP group that is dedicated to being local, but I can't remember.. But yeah, your IP should show there, so tell your router to forward Port 80 to that IP. If it still doesn't save, try updating the firmware on your router.