It's a ".onion" address.  You have to use and install something called Tor (http://www.torproject.org/) to get to it.

Once you've installed Tor and configured it correctly, go to this URL: *Link Removed* .  The URL won't work unless Tor is running and configured.

As an aside, Silk Road seems to be down at the moment... but it was up yesterday.  It seems to go up and down at odd times...