what determines which packages are 'loaded'?

[Charles Crisler]

Hello! I have pkg-config version 0.23 active on my Linux FC9 system. I
am trying to build some software but the autoconfig is failing because
pkg-config can't find specific packages. When I looked at
the /usr/lib/pkgconfig directory I realized that there are MANY more .pc
files than packages that show up from the --list-all command. It turns
out that some packages that are 'missing' actually have .pc files in the
proper directory. I have looked at the files and can't see any
significant difference between pc files for libraries that aren't listed
and those that are. I have also looked at the man page and still don't
have a clue why it isn't working. This is a really convieniant utility,
I just wish it worked better. Can/would anyone shed some light on what
might be happening? TIA, Chuck Crisler