I've got 2 Ruby versions: 1.8.7 and 1.9.2 and PostgreSQL 8.3. I cant install pg gem on any of them. Getting this error:

C:/Development/Ruby187/bin/ruby.exe extconf.rb
checking for pg_config... yes
not recorded
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
 --with-opt-dir
 --without-opt-dir
 --with-opt-include
 --without-opt-include=${opt-dir}/include
 --with-opt-lib
 --without-opt-lib=${opt-dir}/lib
 --with-make-prog
 --without-make-prog
 --srcdir=.
 --curdir
 --ruby=C:/Development/Ruby187/bin/ruby
 --with-pg
 --without-pg
 --with-pg-config
 --without-pg-config
 --with-pg-dir
 --without-pg-dir
 --with-pg-include
 --without-pg-include=${pg-dir}/include
 --with-pg-lib
 --without-pg-lib=${pg-dir}/lib

I know it's a common problem, but I haven't found any working solution yet... Oh, I have added C:\Program Files (x86)\PostgreSQL\8.3\bin to my PATH.