These ebuilds come from https://github.com/anyc/steam-overlay.
If you have some problems, go to the official site first.
steam-runtime-bin : Precompiled 32bit libraries for steam that are currently missing on AMD64 ( http://github.com/anyc/steam-overlay/ )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a steam
For Paludis use this rsync : rsync://gentoo.zugaina.org/steam-portage
If you have a problem : ycarus(-at-)zugaina.org