Hi,
I have set up this combination on various platforms, including Windows, FreeBSD, RHEL and CentOS and I must say that by far the easiest was CentOS.
Down below follows the general procedure (based on CentOS 4), and if that doesn't help, feel free to ask some more specifics.
Firstly, much will depend upon which type of CentOS installation you performed: full, desktop or server. If you installed the system with all packages, there's very little to add lateron. If, OTOH, you chose one of the other options, you are likely to have to install some more packages.
Assuming you have performed a very basic installation, you'd typically need to perform the following calls (you can use yum or up2date for this):
up2date php mysql httpd up2date mysql-server php-mysql
[Note: you can check the presence of these packages by performing: rpm -qa | grep <package name>, e.g. check the output when performing rpm -qa | grep mysql]
Once these packages are installed, you're almost done. You'll need to make sure the MySQL daemon gets started at boottime (or at least: that's what I always do as I don't want to have to start it manually), which can be achieved by the following: /sbin/chkconfig mysqld on
Make sure to do the same for Apache: /sbin/chkconfig httpd on
Now, Apache will not start using it's default httpd.conf file, so you'll have to edit that: vi /etc/httpd/conf/httpd.conf
Now, search for the ServerName directive and set that to your machine's IP address, or fully qualified hostname (e.g. ServerName 192.168.1.1:80). Scroll down a bit and set the UseCanonicalName directive to On (default = Off). Save your changes.
That's pretty much it. You can start Apache manually to make sure the config file is correct, by typing (as root): apachectl start
If all goes well, you should now see a set of httpd daemons when running top (or ps -ef | grep http).
Now, test your installation, by pointing a browser to the IP address (or fully qualified hostname, ot just the localhost) to test if Apache indeed is running.
Finally, I at this point in time I always reboot the machine one to make sure everything comes up properly at boot time.
Once this is done, you should be all set, and then you can start using PHP and MySQL as well. Please let me know if you need some help getting that running/tested as well...
Cheers! Olafo