'Digital stations' are illegal without a licence, and you need to be part of a multiplex anyway (i.e. like the BBC ones) so you need to be 'official' to do it.

Internet radio however is completely legal and free to everyone to listen too. There is some question about PRS licenses, but I don't believe MCPS/PRS have any hard and fast rules about internet broadcasting yet.

All you need is a broadband connection to broadcast (to be on the safe side) and you just load all the tracks you want to play into an mp3 program like iTunes or winamp. I've tried some test broadcasts from home, and I actually pre-recorded the whole show (including links) the hour before I put it on air, but you can drag and drop in real time to cue tracks. Incidently, having not told anyone I was doing it that evening other than my housemates, I got five extra spontanious listeners according to the statistics window of the software - and one was in Alaska.

The software I used was shoutcast.