The beeb has a very slick iplayer for UK residents that lets them tune in to radio or tv on computer & at their convenience.
http://www.bbc.co.uk/iplayer/

Unfortunately its not yet available to those outside the UK, but check this out:
"However, BBC Worldwide is working on an international version, which we will make available as soon as we can and will make an announcement nearer the time."

Radio is available now: http://www.bbc.co.uk/iplayer/radio