right now if you type in the IP you have into a browser, it'll load that default installation apache page. Your web server is running, and is world readable. I assume you already knew this, but I just wanted to make sure just in case. Sorry if that sounded kinda pedantic.
You're going to need the php-mods for apache to build your testbed, but knowing how Slack8 default installs, they're probably already in there. If you don't want the webserver to be publicly viewable at all, I think you can bind it to the loopback address, but its probably just easiest to have it listen to some bizarre port number like 30000 or something way past where 3l33t script kiddies usually scan. Its all really a matter of changing your /etc/apache/httpd.conf file to your liking and killing and restarting the daemon.
grepping through mine I found:
fin@horatio:/etc/apache$ grep php httpd.conf
#
http://www.php.net) will typically use:
#AddType application/x-httpd-php3 .php3
#AddType application/x-httpd-php3-source .phps
#AddType application/x-httpd-php .php
#AddType application/x-httpd-php-source .phps
# ==> mod_php configuration settings <==
#Include /etc/apache/mod_php.conf
This will probably be pretty easy, although I've never played with php before, so I may be full of it.
Luck,
Finegan