I finally got arount to compiling OpenCV on my G4 Mac mini. While there is a lot of good information online as to how to do this, there were a few final steps that took me a while to either figure out or find. Apparently using OpenCV on OS X is still a new thing...
First of all, follow the directions here at the Mac OS X OpenCV Port Wiki. (Note the two different configure options for Fink and MacPorts/DarwinPorts)
Then, after typing "sudo make install", the include files should be in /usr/local/include/opencv, while the dynamic libraries should be in /usr/local/lib.
So, the last thing to do is let your shell know about the libraries, and pkgconfig. Since I use bash, I added this to my .bashrc file.
And so... things seem to work.
Many thanks go to those who've done a lot of work to get OpenCV on OS X!