Friend
Just install the library requirements (libcurl and libxml2), setting
environment variables PKG_CONFIG_PATH and LD_LIBRARY_PATH to their
locations before running 'configure'. Then, its just 'make' and 'make
install' (thanks to autotools magic!).
You can use fink to install the dependency libraries (or just download
the tarballs and compile the source code).
Best regards
Adenilson
ps: I also suggest you to use the git repository version of libgcal,
it has some new functionalities, like raw XML mode (i.e. using only
XML instead of gcal_event/gcal_contact types) and bug fixes. I'm
planning to do a libgcal 0.8 release in the next month.