Well I don't think an Offline server is going to show in the list in the first place, so you're probably going to need to join by IP address. If you guys really do have the same IP then you'll need to use the local IP.
To find out what your local IP is, click the start button and type 'cmd' in the search box to open the command prompt if you're in Windows 7, if you're using Windows XP click on run and then type it.
Once the command prompt it up type ipconfig and hit enter then find the line that says IPv4 address. Odds are it'll start with a 192 though it might also be 172 or 10.
Have your friend go to Join Game (Specify IP) and type that in to join your server.