There is no longer a Gentoo ebuild for xmms. I was a little bit surprised, looked up bugs.gentoo.org, didn't find any information about it. That's why I now abuse bugs.gentoo.org ... Feel free to close thee bug, and please accept my apologies for filing it in the first place. ;-)
The story behind it can be read in the thread http://thread.gmane.org/gmane.linux.gentoo.devel/41635 or here: http://comments.gmane.org/gmane.linux.gentoo.devel/43518.
If you miss xmms on your system (I do), just go to http://www.gentoo.org/, download the sources, and compile it yourself. It worked here with no problem (don't forget to run "ldconfig" after "make install"). If you know a better way (overlay?), please describe it in a comment to this "bug".
Maybe you can leave this bug open for a month or two, so that people will find a link to some background information here, why xmms is no longer available as a Gentoo package.
*** This bug has been marked as a duplicate of 152472 ***
My personal opinion:
I personally miss xmms. Wouldn't it have been possible to just mask it? It compiled and worked here out of the box, so it doesn't look like a completely broken package to me.
Using a package is something completely different than maintaining it for a *nix distribution, that is perfectly understood. But maybe somebody can describe why xmms is such a nightmare to maintain? And a rough description on how to continue using xmms with Gentoo would also be highly appreciated.
This isn't a bug and this isn't the right place for this please don't comment anything more here. You should see the gentoo mailing lists, forums and weekly news. This url might help you http://www.gentoo.org/proj/en/desktop/sound/xmms.xml
There's a few overlays that as xmms that you can use.
Thanks for understanding