I have apache 1.3.6 installed (linux) and it works fine with localhost.  I want to learn apache, perl, php, etc., but do not have a domain name (no isp)and am not part of a network. What is the best set up to simulate a web site on a single box - the O'Reilly book discourages one from using localhost and uses an intranet as an example.  

Thanks in advance.

I've recently set something similar up (laptop with cheap PC-Card NIC that isn't recognised by Linux).  The first thing I had to do was get DNS running, and add a "CNAME" entry pointing "my.madeupname.com" at "localhost".

Then Apache refused to start because it couldn't resolve it's own FQDN.  Adding "ServerName my.madeupname.com" to the httpd.conf file solved this, and I can connect to the server as "http://my.madeupname.com"; or "http://localhost";.

However, having done all that there's no really compelling reason to do this if you just want to learn Apache/Perl/PHP.  Using "localhost" should be fine.  I had to do the things above because I was also installing, configuring, and generally looking at qmail, which needs DNS to be running.  The Apache set up came about the next time I rebooted and Apache stopped working...

Probably best if you stick to "localhost" for now.