Offline Bukkit Server, Need Help

I am trying to get an offline Bukkit server running but I am having some problems. I have to set up a LAN from my computer because my internet does not let me use servers on it, here are my problems:
Every time I put in my Ipv4 address into the settings, when I start the server it says failed to bind port, I did not think you need ports for offline and here's my properties

#Minecraft server properties
#Sun Sep 25 11:33:30 BST 2011
level-name=world
allow-nether=true
view-distance=10
spawn-monsters=true
online-mode=false
difficulty=1
gamemode=0
spawn-animals=true
max-players=20
server-ip=(my IPv4 address)
pvp=true
level-seed=
server-port=
allow-flight=false
white-list=false
motd=A Minecraft Server

Also, when it does work, which is not very often, I connect then my friend connects and it kicks me out because it says my friend has the same IP as me. Is this because he is connected to my computer's network?

Please Help

 

you have to use your INTERNAL IP

Your LAN connection has an IP .. use that. Or run CMD in startmenu and type ipconfig.. you see your connection there. USe your LAN ip and pass it your friends. Or just type localhost in the IP requirement space in the server.properties file and connect to your server with the ip localhost. But only you can connect with localhost ip.

 

I was using my LAN IP, on cmd it says Wireless LAN adapter Wireless Network Connection:
then underneath it says Autoconfiguration IPv4 Address: then it says the IP I use. We are able to connect to the server but only 1 person can be on at a time because we apparently have the same IP when we are connected.

 

Just leave the field blank. You should only put an IP address there under a few specific conditions which you do not fall under.

 

How do I connect to it then?

Or my friends to connect

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

With your external IP address (it should not start with a 10. or a 192.). If you are using Hamachi, it should start with 5. However, I don't think you are using Hamachi.

 

No i'm not using Hamachi, how do you find out your external IP, I can't find it on cmd

 

http://www.whatismyip.com/

 

My friend still can't connect even with the external IP.

 

Then you set up port forwarding incorrectly.

 

But this is offline and I can't access the router setup because it isn't mine and they've changed it from the default

Ok. I have the connection thing fixed and me and my friend can connect... but not at the same time. Every time he connects it kicks me out because when we connect we are automatically just called Player, so we have the same name and it doesn't work.

Thankyou for all your help, it works!

EDIT by Moderator: merged posts, please use the edit button instead of double posting.