The AlienAddons change on AlienBBC isn't working for me. Not quite sure why. I've hacked BBC Wales into the plugin.pm for the time being until I've got time to go through the code.
Install slimserver. I used the debian.slimdevices.com build but had to download the complete package to get the build-perl-modules.pl script. The .deb builds into /usr/share/slimserver rather than /usr/local/slimserver as per the instructions
Install the mplayer essential codecs in /usr/lib/win32 (got the location from watching /var/log/slimserver/slimserver.log whilst trying to start a stream)
The final bit (which wasn't obvious!) was that I needed to install libstdc++5 package and a c++ compiler. Found that by running: mplayer rtsp://rmlivev8.bbc.net.uk/farm/*/ev7/live24/radio1/live/r1_dsat_g2.ra