A little googling yielded something interesting, though.
[link|http://publib-b.boulder.ibm.com/Redbooks.nsf/RedpieceAbstracts/redp3639.html|http://publib-b.boul...cts/redp3639.html]
"Note: PHP is not supported on the iSeries by IBM. We have provided these instructions for you to be able to download a public domain open-source copy of a PHP engine to allow you to run PHP scripts on the iSeries."
Given that, then [link|http://freshmeat.net/search/?q=CMS&trove_cat_id=183§ion=trove_cat&Go.x=0&Go.y=0|this]?

I know - the unsupported bit is bad. I still thought it was interesting...