Do this:
Instructions for use:

su -
mkdir /usr/local/mythtv_portage
git clone git://github.com/MythTV/packaging.git /usr/local/mythtv_portage/
ln -s /usr/local/mythtv_portage/Gentoo/scripts/selfupdate /etc/portage/postsync.d/updateMythEbuilds

edit /etc/make.conf
add /usr/local/mythtv_portage/Gentoo to PORTDIR_OVERLAY
eg

PORTDIR_OVERLAY="/usr/local/mythtv_portage/Gentoo"

I will post if I have any problems media-tv/mythtv-0.25_pre20111129.
* MythVideo is now streamlined into MythTV, so no need for the separate package.

Don't forget to add packages to the packages.keywords file.
www-apps/mythweb
media-tv/mythtv
media-plugins/mytharchive