MP3 sharing?

[noirist]

Is it illegal to share MP3s, for previewing purposes only?

I would like to create my own MP3 rotation site to promote artists whose music I enjoy, by uploading 1 song of theirs (not available as a single!) to introduce their music to people who may not of heard of them.

I would include a disclaimer and all that, but don't want to do anything before I know if it is acceptable or not! >.<

Thanks to anyone who can help.
x-posted to music.