Click start, go to run. Type cmd and press enter.
Type ipconfig and press enter.
It should say something along the lines of Ethernet adapter Local Area Connection: blah...
Look for your IP address. Mine happens to be 192.168.1.104. Yours will probably be similar.
Then try direct connecting using the local IP of whichever computer is running the dedicated. If you are hosting the dedicated server on your computer, it will be your IP. If you are joining it on the computer your dad is running, it will be his IP.