These ebuilds come from http://github.com/sjnewbury/multilib-overlay.
If you have some problems, go to the official site first.
gtk-engines : GTK+2 standard engines and themes ( http://www.gtk.org/ )
gtk-engines-murrine : Murrine GTK+2 Cairo Engine ( http://www.cimitan.com/murrine/ )
gtk-engines-xfce : Xfce's GTK+ engine and themes ( http://www.xfce.org/projects/ )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a multilib
For Paludis use this rsync : rsync://gentoo.zugaina.org/multilib-portage
If you have a problem : ycarus(-at-)zugaina.org