first off, thanks for the instructions in here on how to build/install a plugin. With those I was able to successfully build our plugin:
I'm part of the Exult team (http://exult.sf.net) and we have a little plugin that loads and saves the Ultima 7 graphics file format shp. Our code is at http://exult.svn.sourceforge.net/viewvc ... it/u7shp.c
When enabling building the plugin in ./configure of Exult, it gets built without a problem on make and it works in The Gimp.
I found that I didn't even need the makefile after all, just a "gimptool-2.0 --build u7shp.c" worked fine as well.
Now that I managed to build the plugin, I wonder if I can build the plugin statically so I can get rid of all the stuff that got installed by MacPorts to install The Gimp. Right now I see in the compiled plugin that it points to various gimp dynamic libs in /opt/local/libs, for example opt/local/lib/libgimpui-2.0.0.dylib