Try this url:
ftp://ftp.gnome.org/pub/GNOME/RHAD/redhat-6.0/i386/glib-devel-1.2.3-1.i386.rpm
You need the *-devel packages for anything you'll compile against. You may
need the gtk-devel-1.2.3-1.i386.rpm at the same location. Also, if you
don't have glib/gtk 1.2.3, you'll probably need the non-devel packages,
too. (gtk-1.2.3-1.i386.rpm and glib-1.2.3-1.i386.rpm)
If that doesn't help, perhaps you could post the revelant output from make
when you try to compile abiword?
Justin