To cut to the quick, here are the steps you need to follow:
Build and install a normal kernel (with DVB and v4l stuff selected as modules).
hg clone http://linuxtv.org/hg/v4l-dvb #(you might need to install mercurial - a cvs replacement)
cd v4l-dvb && make && make install
Grab some firmware:
DVB_CARDS="tda1004x" emerge -v media-tv/linuxtv-dvb-firmware
Reboot (optional, but suggested).
Then, when it comes back:
modprobe -v saa7134 card=104 && modprobe -v saa7134_dvb
dvbscan /usr/share/dvb/scan/dvb-t/uk-yourlocation > ~/.mplayer/channels.conf
mplayer dvb://Film4
For the rest of the whole thing, see the post Linux driver support
