i guess you could try to use any one of these commands to see if perl is installed.
on my system, whereis perl and which perl will output /usr/bin/perl which is where the perl program is at. my guess is though that perl.h file is a c/c++ file, in which case, when you installed mandy, did you choose to install the development packages? i'm not sure on how mandy's install is since i don't use it, but i know in redhat's install, you can make a choice of the different packages you want installed, one of which being the development packages needed for compiling programs/source code. if you didn't, try finding the packages on your mandy install cds.