Tor project has just released a portable free proxy program, which has Firefox included which doesn't need any installation or admin privilages.
This will only work if your school/college allows useage of Pen Drives/ CD's.
Go to Tor: anonymity online
Click on the Downloads Tab
Download Tor Browser Bundle for Windows.
Plug your pendrive into your computer. Then run the Tor Setup, Choose your location of your pendrive to extract to. Then all you need to do is when your at school, plug your pendrive in and run Tor Browser.exe and it will set itself up and you can bypass any blocks. Its really useful if your college blocks Hotmail, Youtube, Facebook Etc.