DNS Host resolution

I am trying to get our host names to resolve by entering (hostname).com in the address bar window in explorer.

I am running Windows 2000 server (Microsoft DNS)
And the web site server is IIS.

I have added the custom http headers on the web site and added host records on the DNS server, but I am still not getting name resolution unless the address is entered as www.hostname.com.

What am I missing?