These ebuilds come from http://mpd.wikia.com/wiki/Repositories#Experimental_Gentoo_Overlay.
If you have some problems, go to the official site first.
librmpd : Ruby library for communicating with an MPD server ( http://librmpd.rubyforge.org/ )
mpd-rb : Ruby class for communicating with an MPD server ( http://rubyforge.org/projects/mpd/ )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a zugaina
For Paludis use this rsync : rsync://gentoo.zugaina.org/zugaina-portage
If you have a problem : ycarus(-at-)zugaina.org