Simply use something known as a "Proxy".
In my own words, a proxy is a web-browser *Not truely*
That acts as a diffrent IP address.
So the school does not block it, its only blocking your schools IP address,
but in reality your useing a diffrent one, and you can get on web-sites such as myspace, youtube.
I do not recommend useing one of these without your teachers permission,
or someone in the schoolboard with higher authority!