Have you tried running a phpinfo check?
Don't forget that php will only work on files in your
Sites folder (i.e. reached via your localhost IP (
http://127.0.0.1/ or
http://127.0.0.1/~user/)
What makes you think that something's not where it should be?
btw, which installer package did you use?
I used the
Marc Liyanage package and it seems to have taken ok.
Looking for "PHP" items now I see that there is a folder at: Volume/System/Library/PHP
That one seems to be the most significant, though there are numerous folders with the name "php" dotted all over, but that is the only one in uppercase.