Compiling with Perl Support

I am trying to build Postgres 6.3.2 on Linux. I would like to build using the
"./configure --with-perl" directive.

The docs say:
---------------------------------------------------------------
--with-perl Enables the perl interface. Note that this
requires an installed version of postgreSQL.
---------------------------------------------------------------

So when I exectute the "./configure --with-perl" and configure finishes, I get
the following:
---------------------------------------------------------------------------
checking setting USE_PERL... enabled
configure: warning: perl support disabled; postgres not previously installed
---------------------------------------------------------------------------

So my question is: why is perl support being disabled when I asked to enable it.
I already have Postgres 6.3.2 running without the perl support compiled in. I
don't quite understand this one and I have read thru the docs as well as scanned
the mailing list archives.

Thanks in advance!

Andy