Throw this in your address bar http://wpad.domain.tld/wpad.dat, where domain.tld is your schools domain. If you're not sure what to put there, and you can run an ipconfig, it will be listed as the DNS Suffex. See if you can figure that file out. Go here to start looking for more information: http://en.wikipedia.org/wiki/Web_Proxy_Aut...covery_Protocol
If that file doesn't exist the problem will be a lot harder to solve. Good luck, and I hope you learn something about how auto proxy discover works. Keep in mind that even if you do find out how to get to the proxy server, your admin will most likely have firewalled off the ports for common IM protocols if he doesn't want you to use them.
Also, I assume they've filtered http://wwwl.meebo.com/
P.S. I am a punk.
