C:>nslookup http://www.facebook.com
Name: http://www.facebook.com
Address: 66.220.149.18
You can use nslookup to get a starting point of the ip block, and look up that ip at arin.net, to get the entire block they use, in this case, those 2 /20 blocks, but there may be more. You could use perhaps iptraf built into Zeroshell from ssh or the console to track traffic for other ips/blocks with a single computer. Or google for known blocks used by a domain.