Newbie Question

[Paul Guba]

OK so I have set up the DNS based on the examples in DNS and Bind book.  
I'm able to nslookup all the computers in my domain.  Not many just four 
computers and a router.  All the names resolve to to the IP addresses 
and vice versa.  However if I do nslookup mydomain.com, nslookup 
www.mydomain.com I get the dreaded can't find message.  Based on the 
book I can't find out what I'm doing wrong.  I am running Bind 8.2.3-1 
on YDL Linux.