Hi, and welcome to the forums!
If you're new to Linux, then I'd recommend SUSE - it's easy to use and is very intuitive. There are other distros which are more locked down out of the box because they were created to be used on servers, but SUSE is a perfectly valid option if this is your first time setting up a Linux server.
The standard version of SUSE will do fine. Make sure the latest and greatest version of Apache is installed (via YAST), along with MySQL and PHP, and then all you need to do is configure the httpd.conf to include the PHP module and whatnot.
Will this webserver be internal (network) or external (internet)? If it is internal, then just installing Apache, MySQL and PHP and setting up Apache to use them will do fine - the web server will then be accessible via
http://name_of_computer/ from any networked computer. However, if you want to setup a webserver for the internet, then you will also have to setup a DNS server. But, I do not advise using a copy of SUSE which is not locked down as an internet server.
If you would like my recommendation, then
EnGarde Linux is a great solution. It is easy to setup, is very secure, and the documentation will have you rolling in no time. Just MHO.
Best of luck, and please let us know if you have any problems!
-jk