For sonic wall access, you have to have a sonic wall administrator account and password, you then have to log on to the SonicWall website (it escapes me at the moment...) but once you log in, you are only given 30 minutes of browsing time.
Besides, school isn't really a good place to take your own laptop. By accessing your school's network, the network administrator now has your informaition, IP address, computer name, etc... You could be severely punished if caught running past the SonicWall.