> OS: Red hat Fedora 5 x86_64
>
> DB: PostgreSQL 8.1.4
>
> I am use PostgreSQL 8.1.4 RPM install my DB
>
> I have download PostgreSQL 8.1.4 source code and compile it.
>
> I try run
>
> ./configure --with-pgsourcetree=/usr/local/src/postgresql-8.1.4/
>
> ./configure --with-pgconfigdir=/var/lib/pgsql/data
>
> ./configure --with-pgconfigdir=/usr/bin/
>
> Error Messages
>
> checking for pg_config... configure: error: Cannot find pg_config.
>
>     Please specify correct installation path for pg_config
>
>     with --with-pgconfigdir=<dir>

Where does the program pg_config reside on your system?

On Debian, I can use the command:

   dpkg --search pg_config to search for where pg_config is...

The results are thus:
cbbrowne at dba2:~$ dpkg --search pg_config | egrep "/pg_config$"
libpq-dev: /usr/bin/pg_config
libpq-dev: /usr/lib/postgresql/8.1/bin/pg_config

Based on that, I could run eithe
r:
./configure --with-pgconfigdir=/usr/bin
or
./configure --with-pgconfigdir=/usr/lib/postgresql/8.1/bin

I'm not sure of the equivalent option for RPM.  In any case, you need to
set --with-pgconfigdir=[directory where pg_config is found]