I worked out how to make a server for me to join, and then finally got the port forward to work and then while screwing around with it i got it to work offline with other computers in my network.
im absolutely no computer expert so im not sure if you guys already worked it out.
this works for mac but im sure theres a way to do it for pc as well.
it works using airport, you go to create network, and get the other computer(s) (i havent tried with more than two, as i only have one account between a few people... , im testing it soon) to join it.
then you go to system prefs>network>airport and the button should be orange, saying self assigned IP or no assigned IP, then you click advanced and TCP/IP and configure IPv4 using DHCP with manual address. (i dont know a thing about what half of these mean, im just reading it off) then put in the IP you want (im not sure about the bounds of the numbers, i had 192.168.X.XXX) after that you change the server IP in server properties to be the same and your all set, as long as your connected to your own network and they are too.
im fairly sure its just making your computer pretend its on the internet, so minecraft thinks it is.
tell me what you think