The Glib library is used as a basic platform abstraction library, it's not related to graphical user interface (GUI) things. For a detailed description about GLib, see Section 6.3, “The GLib library”.
The GTK and it's dependant libraries are used to build Ethereal's GUI. For a detailed description of the GTK libraries, see Section 9.2, “The GTK library”.
All other libraries are dependant on the two libraries mentioned above, you will typically not come in touch with these while doing Ethereal development.
As the requirements for the GLib/GTK libraries increased in the past, it depends on the GLib/GTK versions you have, which additional libraries are required. The 1.x versions only needed GLib/GDK/GTK+, while the 2.x versions require all mentioned libs.
The GLib/GTK+ libraries are available for many unix-like platforms and cygwin.
If these libraries aren't already installed and also not available as a package for your platform, you can get them at: http://www.gtk.org.
You can get the latest version at: http://www.gimp.org/%7Etml/gimp/win32/downloads.html.