Automatic playback of mp3 when someone nearby

I am a newbie to arduino and I am looking into a project where I want a motion sensor or ultrasonic range meter to trigger the playback of an mp3 file, e g when someone passes they hear a sound. Preferrably amplified through an external sound system. Any tips on how to go about? Has anyone documented anything like this before?

Use the search box at top of this page "sense and play MP3"

Weedpharma