Where is libpq-fe.h?

Im trying to install DBD-Pg so that I can connect to pgsql databases
through Perl.

The README files say I should set some environment variables.. quoting
the readme file:

"...The Makefile checks the environment variables POSTGRES_INCLUDE and
POSTGRES_LIB, to find the library libpq.so and the proper include
files."

Not knowing what the 'proper' include files were I guessed at a
directory in the pgsql installation.

perl MakeFile.PL worked fine - No errors

however 'make' got so far and gave a fatal error saying it cant find
file libpq-fe.h
Looking for this manually and using " find . -name libpq-fe.h " I dont
come up with anything, either in the postgres installation or the perl5
installation. should the file exist? Without it I cant install these
perl modules and cant see a way of getting any further. Has anyone had
a similar problem theyve managed to get round? Any help would be
appreciated.

I also tried installing the Pg module (as apposed to the DBD-Pg module)
and found the same problem.

Any help would be very much appreciated.

Barry