[p0lar_bear]

Simple.

First, download the slim version of the XSPF player from http://musicplayer.sourceforge.net/.

Upload the player to somewhere on your site or forums. For example purposes, upload a short and/or low quality MP3 with it.

Next, create a new bbcode tag. Use something like this:

Title: MP3 Embed
Tag: mp3
Replacement:

<object type="application/x-shockwave-flash" height="15" width="400" data="http://path.to.your/player/xspf_player_slim.swf?song_url={option}&song_title={param}&player_title={param}">
<param name="movie" value="http://path.to.your/player/xspf_player_slim.swf?song_url={option}&song_title={param}&player_title={param}" />
</object>

Example: [mp3="http://path.to.your/player/example.mp3"]Pearl Jam - Even Flow[/mp3]
Description: Embeds a slim player into a post that plays a specified song, showing the specified title.
Use {option}: Yes