Wow this was old school.
Update May 2012-
I would have a bootable USB stick and run a pocket LINUX version today. Or if USB Boot is disabled in the BIOS then the Phone tether method also works with USB or wirelessly. Then you have no filters, blocks or issues. You can install anything and run it to access the network.
Now that everyone has phones with internet service is no big deal to get to your mail and webpage anymore.
It is cheaper to use WiFi calling or surfing than 3G or 4G services, so look for open or public WiFi and use your phone connected and preferenced to WiFi at home, work or mall etc.
Stuck at school? Setup your phone to VNC or RDC "remote" into your computer at home. Then just control from anywhere.
Grounded, cut off....awwww. Even game consoles can run LINUX. If you have anything with a CPU someone has unlocked it.
At school, in a library or mall and have access to a PC but cannot "surf" to any thing but their one site or a "filtered" subset of the internet?
Is Youtube blocked?
Is iTunes, Bittorrents or other sites blocked?
Can you not download or installed software?
Ok...we'll try to help you dorks out.
Step 1: Overview
Many types of 'blocks' are placed on schools and publics computers...however they have limited funds and can also be open to social engineering....
They have to block ALL exploits and all access to command line, process startup/control and downloads...plus keyboards, admin roles, powerusers or even USB ports and BIOS firmware!
if ANY of these are exploitable then we have means to attempt to access any system's internet access....or a cooler idea is to enable a PC's "ICS" Internet Connection Sharing, or peer-to-peer wireless 802.3 even Bluetooth and use your Bluetooth or WiFi phone, pda or itouch to then surf 'unobstructed' ! hehe
I'll provide follow-up steps for EACH below as time permits.
1) Simple browser filter or cheap software like netnanny etc.
We exploit this with a proxy or web redirector and kill -f process name or id
2) Advanced Network filter and site blocking
Many proxy or redirector will bypass these as well, where they do not we also use advanced proxy services like the Vidalia bundle , TOR, Prioxy & Vidalia
3) Keyboard disabled or missing
OH soooooo easy, Microsoft allows for "disabled" users with an on-screen keyboard! duh
4) Kiosk Mode IE
OMG even easier! ALT+f4 logs off IE and then start whatever you want as above or see below....
5) Starting and stopping processes, killing or modifying msconfig etc
helpful for custom downloads or setup of exploits above
6) Basket / Corner cases
tough nut? Post your isseus
You need to research the environment, use human engineering develop specific exploits and then go get 'em...