Do you know for a fact that the proxy server is in fact Squid? The nature of the proxy server changes the approach.
School law can get quite complicated (and IANAL), but the bottom line is that the school district is responsible for making a best effort to appropriately filter content (which is the reverse of standard college policy). That means that the school needs some way of constantly updating which sites are accessible (unless of course they just throw their hands up and institute a very strict whitelist policy, which they might have done if they are just using Squid). In many organizations, a dedicated proxy device is used that subscribes to a service which constantly updates web site categorization. These services have gotten very good over the years at detecting and preventing the standard sorts of ways around your institutional proxy (such as setting your own proxy server up outside the network and using that to view Stack Overflow, which is essentially Bruno's answer).
It is possible to use VNC over an HTTP proxy, which might accomplish what you want (remote into your outside machine and then run a web browser inside it). I have also seen some people have success with SSH tunneling through HTTP proxies (Craig notes that it shouldn't work, and maybe it doesn't with Squid, but I have seen it done with other proxy devices although I've never tried it myself). Again, unless they really are using a fairly static Squid configuration, don't be surprised if the admins catch on fairly quickly as to what you are up to.
Since I am, in fact, employed to prevent precisely the kind of thing you are describing, I should note that violating your institution's Acceptable Use Policy will get you into a lot of hot water. Yes, you said to ignore the ethics but this post is appearing under my name and will be eminently Googleable. :)
That said, even when I was a student and not an employee, I found that some problems are best solved organizationally. There is a procedure somewhere for unblocking websites, and there are people authorized to submit to that procedure (i.e. teachers, professors, etc.). If you can make the case to them that some sites should be unblocked, then they can make the case to the IT Department. Provided that no one has previously offended the BOFH, you should be able to get access to the site. After all, it is quite well known and dedicated to intelligently solving technical issues rather than trading ways of attacking your network.
