"The server does not have a DNS entry" errors

"DNS" stands for "Domain Name Services", which is the method used to
translate the name of a computer system (which is easier for humans to
remember) into its numeric IP address (which is needed by any computer
trying to connect to it).  The "server does not have a DNS entry" error
means, fundamentally, that Netscape Navigator was not able to find a DNS
name server on your network which could find an IP address corresponding
to the name you gave.
If you get a "The server does not have a DNS entry" error when you try
to access a certain web server, then this could indicate any of several
problems:
Most often, this means that there was a momentary network problem --
perhaps your network or your domain name server was too busy to handle
your connection attempt.  If you try a second time to connect, sometimes
the connection will then go through properly.  If this happens to you
often, then you might want to try connecting during off-peak (less busy)
hours, such as in the morning; also, make sure your system
administrators know about the problem.
Sometimes this happens because your computer network is inside an
Internet firewall, and you need some sort of authorization in order to
access the outside world.  You may need to go into the Netscape
Preferences and tell Netscape Navigator to use a "proxy server".
Contact your local system administrators to see if this is the case.
Another reason for this might really be that the server you're looking
for doesn't exist, because you've typed its name incorrectly, you were
given the wrong name to use, or the server is down right now.
This error might also occur because your computer's TCP/IP software
isn't set up properly (usually this wouldn't let you get through to any
web sites at all), in which case you should check it out.
Your network might be set up to use only NIS name mapping instead of
DNS, in which case you will not be able to use hostname with the
Navigator at all.  Netscape Navigator only supports DNS, not NIS.