Sources for glib are available from gnome.org via cvs.  See cvs
checkout instructions at http://www.gnome.org - or use

export CVSROOT=:pserver:anonymous@anoncvs.gnome.org:/cvs/gnome
cvs login (no password)
cvs -z3 checkout glib

or grap a package of the sources we're currently using from
ftp://ftp.mozilla.org/pub/mozilla/libraries/source/

These sources correspond to the GLIB_1_2_0 tag on the gnome cvs
server.
