thats kind of a subjective question. it depends on how detailed you want the members only section to be.
-a gateway to get to a section or page
-a membership type setup where users register and you track them and such
if you are looking for the former, complex and full of features, heres a good tutorial http://php4all.org/?nav=tutorials&showtut&tid=56&cat=PHP
if you want the latter (more basic/ a per page type thing) you can look to this tutorial http://howtocode.net/tutorials/phpMemberSystem.php
a great site in general for tutorials is http://www.phpfreaks.com/tutorials.php
and of course I am just assuming you want to make it with php, there are other options out there. I think theres a way in the dreamhost panel to do a simpler, but just as good, job of it.