Vista Tutorial - Use PC Speakers To Play External Audio Souce (DAB radio for exampl

Hi, I want to use my laptops internal speakers to play music stuff from my
(portable) DAB radio, I have connected it to the line-in socket and been able
to record the music from the DAB radio, but have been unable to have it play
directly to the laptop speakers.
I understand that the microphone and line-in are muted by default
(understandably!) and would normally be de-muted through the levels tab of
the playback devices settings, unfortunately only the speaker volume appears
in the levels tab and nothing else, can anyone advise me why this might be
and how I might be able to sort it out?