Disclaimer:  I've spent most of a week attempting to get my laptop to have a working Linux+Apache+PHP+PostgreSQL on it, and am not there yet.  Compile errors from incompatible versions of the 4 packages being compiled with old/new gcc versions and libstdc++ versions and binutils versions and rpms are sending me in circles, and with only 300M for /usr, I get to rpm -i, rpm -e, rm, and cp over and over and over. :-(

The good news is, I've learned a lot, and one nugget of info that I think solves an old, old, old compilation problem my ISP and I had:

I think I've finally figured out why RedHat 5.2 postgresql rpm and some folks compiling from source get an error involving libpq:

Step 1.  Start with a fresh, bare Linux, with no gcc.
Step 2.  Install gcc LANGUAGES=c, but don't include the libstdc++
(pretend you're naive or short on drive space or just missed that line in the way-too-large gcc install/readme)
Step 3.  Compile postgresql 6.3.2 (or 6.4.2), I think.  Ignore that warning about C++.  It's just a warning.
Step 4.  Compile PHP, get bitched at about c++
Step 5.  Install libstdc++ (or whatever it is)
Step 6.  Compile PHP again.  libpq++ is broken.

PostgreSQL can survive without c++, but leaves out the optional libpq++ part.
Then, PHP can't survive without c++, so you go install it, but now PHP can't compile with the technically valid PostgreSQL because it is missing the libpq++ part.

I can't be sure this is what is really going on, but it seems to fit the cycle I went through to get PHP to compile, though not with PostgreSQL yet.

Ideally, the configure/make scripts would detect this condition and make you recompile PostgreSQL, or maybe scrappy could make PostgreSQL yell louder about c++ or how to install it or something...

Need sleep.  Sorry if this is a totally bogus report.