Can't ping by hostname only by IP address

[Dave Martini 1]

I just installed RHEL WS 3.0 and I can ping other hosts in my subnet
by IP address but not by hostname.

The hosts file in my /etc/nsswitch.conf file looks like this

hosts:      files dns

I have one IP address of one of my DNS servers in the /etc/resolv.conf
file.

But when I type

ping hostname 

it says "unknown host"

Is there some other file I need to update?

Thanks a lot!
Dave Martini
LLNL