I have been able to successfully install FreeImage and Image_Science but I can't guarantee the results. In my situation, my image uploads seem to be a bit broken. Although FreeImage and Image_Science do install successfully as far as I can tell.
This was my stopping point last night, so I have not investigated further. I plan to today. However, your mileage may vary.
I filed a bug report at: http://rubyforge.org/tracker/index.php?func=detail&aid=15093&group_id=1513&atid=5921
Also these patches to ruby seem to have made it into macports already.. more info here: http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/12895
which will give you info on why ruby segfaults etc..
I grabbed the macports source tarball and compiled it, then ran "port selfupdate" then when I built ruby the patches were applied.
When installing the dev tools make sure to have installed 10.3.9 SDK (it's not selected by default)
after building ruby and rb-rubygems with macports I installed FreeImage from source and edited the Makefile.osx but if you are using MacPorts to install FreeImage you can go ahead and attempt to install it or just download it and edit the Makefile.
if you attempt to install it, which is fine... it will fail with..
ld: library not found for -ldylib1.10.5.o collect2: ld returned 1 exit status make: *** [libfreeimage-3.9.2.dylib-ppc] Error 1 make: *** [all] Error 2
and change this:
LIBRARIES_PPC = -Wl,-syslibroot /Developer/SDKs/MacOSX10.3.9.sdk LIBRARIES_I386 = -Wl,-syslibroot /Developer/SDKs/MacOSX10.4u.sdk
LIBRARIES_PPC = -Wl,-syslibroot /Developer/SDKs/MacOSX10.3.9.sdk/usr/lib LIBRARIES_I386 = -Wl,-syslibroot /Developer/SDKs/MacOSX10.4u.sdk/usr/lib
then install it again "port install FreeImage" it will install fine, but maybe an error about cleaning up the build dir, don't worry about it..
You should be okay to install ruby, rb-rubygems now and image_science etc.
which I should probably update since i have made progress since.