Apparently only shows uploaded after the Mac Desktop iPlayer was released will be available for download. So eventually it will work itself out. If you check the latest "Survivors" that is available as well.
You gotta download the BBC's iPlayer Desktop, which may mean you have to install Adobe AIR if you haven't already.
Also, it may say Inter based Macs only, but I have it running with no problem thus far on my G4 eMac