probally not because the proxy server that your school uses blocks the aim port, 5190. you can try a few things called anonymous browsers.
my brother uses this one, http://www.bitty.com/manual/?contentvalue=kevinrose&contenttype=digg;username and he is able to go to any site, with it.
as far as getting aim or aim exresss to work, i wouldn't even wast your time, because what it is going to take to do it, is not worth the risk.
though if you can dial out using a dial-up modem or your "CELL PHONE" hint hint then you could do it.