Gentoo offers ebuilds for kdenlive at http://packages.gentoo.org/package/media-video/kdenlive [1].
A basic install of KDE4 is needed, check the Gentoo KDE 4 Guide [2] if necessary.
Links:
[1] http://packages.gentoo.org/package/media-video/kdenlive
[2] http://www.gentoo.org/proj/en/desktop/kde/kde4-guide.xml