I was just about to post about this so might aswell post here...
My school computers has RM SafetyNet Plus which filters websites. I thought it might be an Internet Explorer addon but i've tried installing Firefox but it still filters. I used Process Explorer to close all programs running but yet again.. it still filters. I don't know how to get rid of it.
If your school computers arn't as strict as mine, you should try doing that ^^