Sucks to be you. Offline mode works perfectly fine for me. I just start up steam, it complains about no connection, I click start in offline mode, poof. Now I can play any steam game I have installed, hassle-free.
It wasn't always this easy, but it is now. go to www.steampowered.com
get on their forums, look around. There are plenty of topics about this, and tutorials on how to configure steam to work properly in offline mode if it isn't.
As for steam not working on your school's campus, you can blame your school for that. They probably block certain ports, possibly with the intention of blocking steam.