Freevo is in the official Gentoo portage tree. To install run
emerge -av freevo
As of 2007-09-11, the above line will install version 1.7.2. Version 1.7.3 is also included in portage but masked. To install 1.7.2 you have to unmask it. You should read theGentoo Handbook to understand how to unmask packages.
The shortest way is to use this command:
ACCEPT_KEYWORDS="~x86" emerge -av freevo
This will install freevo and all it's dependancies, but the next time you do a "world" upgrade emerge would try to downgrade it to it's stable version.
To unmask freevo in a permanent way you have to edit the file /etc/portage/package.keywords (create it if you don't have one) ad add, one per line, the name of the package you want to unmask complete with it's category, followed by the keyword you are unmasking (ex. ~x86).
For instance to unmask pylirc, add
to unmask a particular version, say pylirc-0.0.4, add