The older tmw versions contained an endianess problem that is now fixed in 0.0.18, so version 0.0.18 should be marked ~ppc. I've tested it and works great.
Here's my emerge info: Portage 2.0.53 (default-linux/ppc/2005.1/ppc/G4, gcc-3.4.4, glibc-2.3.5-r2, 2.6.13-gentoo-r3 ppc) ================================================================= System uname: 2.6.13-gentoo-r3 ppc 7447A, altivec supported Gentoo Base System version 1.6.13 dev-lang/python: 2.4.2 sys-apps/sandbox: 1.2.12 sys-devel/autoconf: 2.13, 2.59-r6 sys-devel/automake: 1.4_p6, 1.5, 1.6.3, 1.7.9-r1, 1.8.5-r3, 1.9.6-r1 sys-devel/binutils: 2.16.1 sys-devel/libtool: 1.5.20 virtual/os-headers: 2.6.11-r2 ACCEPT_KEYWORDS="ppc" AUTOCLEAN="yes" CBUILD="powerpc-unknown-linux-gnu" CFLAGS="-O2 -mcpu=G4 -mtune=G4 -maltivec -mabi=altivec -pipe -fomit-frame-pointer" CHOST="powerpc-unknown-linux-gnu" CONFIG_PROTECT="/etc /usr/kde/2/share/config /usr/kde/3.4/env /usr/kde/3.4/share/config /usr/kde/3.4/shutdown /usr/kde/3/share/config /usr/lib/X11/xkb /usr/share/config /usr/share/texmf/dvipdfm/config/ /usr/share/texmf/dvips/config/ /usr/share/texmf/tex/generic/config/ /usr/share/texmf/tex/platex/config/ /usr/share/texmf/xdvi/ /var/qmail/control" CONFIG_PROTECT_MASK="/etc/gconf /etc/terminfo /etc/env.d" CXXFLAGS="-O2 -mcpu=G4 -mtune=G4 -maltivec -mabi=altivec -pipe -fomit-frame-pointer" DISTDIR="/usr/portage/distfiles" FEATURES="autoconfig candy distlocks sandbox sfperms strict" GENTOO_MIRRORS="ftp://ftp.rnl.ist.utl.pt/gentoo" LC_ALL="en_IE.UTF-8" PKGDIR="/usr/portage/packages" PORTAGE_TMPDIR="/var/tmp" PORTDIR="/usr/portage" PORTDIR_OVERLAY="/usr/local/portage" SYNC="rsync://rsync.gentoo.org/gentoo-portage" USE="X alsa altivec animation apm artworkextra bitmap-fonts browserplugin cdr cups dbus dga dhcp dvd eds encode esd firefox foomaticdb gnome gpm gstreamer gtk gtk2 gtkhtml hal howl jikes jpeg mad mikmod mono mozsvg mp3 mpeg mppe-mppc network new-login nls nptl nptlonly nsplugin offensive ogg oggvorbis openal opengl pic png ppc ppds print samba sdl ssl theora truetype unicode usb vorbis xml2 xvid zlib userland_GNU kernel_linux elibc_glibc" Unset: ASFLAGS, CTARGET, LANG, LDFLAGS, LINGUAS, MAKEOPTS
0.0.18.1 added to ~ppc