HTML5 Audio: How to Play only a Selected Portion of an Audio File (audio sprite)?

I think there are a couple of problems here.

Firstly, you're adding an event listener every time the user clicks Play 1.

Also I think

if (currentTime >= 0.5) { ...

should be

if (audio.currentTime >= 0.5) { ...

This also works:

<audio id="sample" src="http://dl.dropbox.com/u/222645/click1sec.mp3" controls preload></audio>

<a href="javascript:playSegment(0.0, 0.5);">Play1</a>
<a href="javascript:playSegment(0.5);">Play2</a>

<script>
var audio = document.getElementById('sample');
var segmentEnd;

audio.addEventListener('timeupdate', function (){
    if (segmentEnd && audio.currentTime >= segmentEnd) {
        audio.pause();
    }   
    console.log(audio.currentTime);
}, false);

function playSegment(startTime, endTime){
    segmentEnd = endTime;
    audio.currentTime = startTime;
    audio.play();
}
</script>