Hi Richard, if they are standard mp3 files, IMO the best way would be to use Moodle's built in mp3 player (which is flash based, much smaller download for folks who don't have a player).
To do that, enable the multimedia plugins filter (filters menu in Configuration). Then upload your mp3 through the links browser (or just ftp them to the course's directory), and link to them via the links browser.
When Moodle renders the page, the multimedia filter will embed a flash player that will handle the linked mp3 file automatically. And the link is still there for folks to click to download the mp3 for folks who's browsers don't support object/embed code.
We're used alot of narration in a current project and this method is performing very nicely.