Ubuntu Networking :: Network Computers Not Accessible By Host-name

For some reason, all the computers on my network can't reach each other via their host names. For example, the ping command doesn't recognize host names:

Code:

$ ping file-server
PING file-server (208.68.139.89) 56(84) bytes of data.
^C
--- file-server ping statistics ---

20 packets transmitted, 0 received, 100% packet loss, time 19152ms However, ping works fine if I use IP addresses instead. I would put the address for "file-server" in my /etc/hosts file, except for the fact that DHCP changes it's address occasionally.I attempted changing the line

send host-name "<host-name>";
in /etc/dhcp3/dhclient.conf to
send host-name "file-server";

but to no avail.