Define 'block it from the internet' though...
Do you want to block it on your computer, regardless of browser used? Or block it for a large group of computers on a network? Or somehow block the Facebook servers from being accessed by anyone?
If you want to simply block it on your computer, you can add "127.0.0.1 facebook.com" to your hosts file (which can be found at %SystemRoot%\system32\drivers\etc\hosts)
Code:
Example hosts file
127.0.0.1 localhost
# Block known malicious websites
127.0.0.1 .archivioadulti.com
127.0.0.1 .internet-explorer.name
127.0.0.1 .katasearch.com
127.0.0.1 .preferiti-windows.com
127.0.0.1 .qoogler.com
127.0.0.1 .tuttoavolonta.com
# Block Facebook
127.0.0.1 .facebook.com
Do it for a network? Use
OpenDNS, change your router to use their DNS servers, and block facebook.com under content filtering. (This also works for individual computers if your network consists of 1 computer connected to a router, or you can set your computer to use OpenDNS manually.
Yes, I like OpenDNS.)
Do it for everyone everywhere? Can't help you there, I'm afraid. (It would probably involve illegal activity.)