Building and installing Gaphor is not a very touch business, at least when you're on a Unix system.
Most GNU/Linux installations come with a recent GNOME installation. Even if you do not use the GNOME desktop, there is a good change that the required libraries are already installed on your systsem.
Make sure the following packages are installed:
| Python 2.2 or newer |
| Gnome-python (also called python-gnome or py-gnome) |
| DiaCanvas2, a library for creating diagrams |
In most cases DiaCanvas2 has to be installed by hand. This can be done by downloading the sources and do a ./configure; make; make install. Make sure the Python bindings are also installed.
Once DiaCanvas2 and it's Python bindings are installed, Gaphor can be easely installed with setup.py: python setup.py install.