you got 2 diferend ip's
1 ip is extern ip that goes back to your provider and the ip you find all over the net
as example , the extern ip can you find on this website
[Only registered and activated users can see links. Click Here To Register...] (my own website :P)
that ip you see is the ip you need to use if you want to get players on your server
then you got a local ip (mostly 192.168.1.X )
the local ip is your ip of your computer
you probaly need to setup your router to point your local ip to your extern ip
thats what they call the DMZ , it opens everything and bypass the router so your local ip becomes the extern ip
now to explain it easy
if you get something like 127.0.0.1 or 192.168.1.X then it is the wrong ip
Greets From PowerChaos