If it is truly a sever there is no reason for not running other standard web services unless you expect a large ammount of web trafic and the same server is also trying to transcode your media files, usually for home use, I don't see this happening. I'm sure someone who is more familar with WHS 2011 will reply soon as its been awhile since I used it on my network as I tend to use linux for my servers. I believe WHS has IIS already installed and you will follow intructions for setting up php and mysql for IIS but If I remember correctly (but this may only be from prior to the 2011 version) generally they are installed on the "d:" drive and/or many references to c:\whatever need to be changed appropriately. I'll see if I can dig it up but there was an article about getting worpress on WHS which was quite informative you may wish to serach for such article, I believe wegotserved has one that also recommended a book for all of WHS 2011
Most searches for help in configuring PHP/mysql will probably be geared towards "LAMP" (Linux, Apache, MySQL, PHP) and little but some changes are necessary when going to "WAMP" as there are subtle differences between linux and windows. In your case you may need to refine your searches to "WIMP"
Is this a learning experience to learn php/mysql or to learn installing/administering them if its just the former, I usually reccommend using something like MOWES portable to start out.