to be more explicit
$ cd /etc/apache2
$ sudo cp -p httpd.conf httpd.conf.bak
I'm assuming you are an administrative user.
You indicated you had 10.5.6, so if you see threads talking about /etc/httpd, that's older versions of MacOSX. And, yes,
$ locate httpd.conf
will generate a list of files that it finds. Note that /etc, which I use, is a symlink to /private/etc.