>>5

1. Get additional box.
2. Install GNAA/Lunix.
3. Install squid proxy.
4. Place box between you and internet, as far physically away from your normal PC.
5. Do not enable packet forwarding.
6. Set your box to go through the squid proxy.
7. Block hosts on proxy box (/etc/hosts should be okay).
8. After beeing done with setup, remove screen/mouse/keyboard from proxy box. DO NOT install any means of remote control (Like an ssh server).

The result:

• You can only use HTTP and FTP.
• You can't go to pages blocked on the proxy box.
• To change anything, you'd have to attach a screen and a keyboard to the proxy box, which is a lot of stuff just for changing something.

If that isn't enough, just set a random password on the proxy box.