here's some code i made. if you play with it some im sure you can eventually get what you want.
<script type="text/javascript">
var date1 = "23-Jun-2004 16:31:38"
date1 = date1.replace("-", " ")
date1 = date1.replace("-", " ")
document.write(date1 + "<br />")
var d = new Date(date1)
document.write(d.getTime() / 1000)
</script>
getTime() returns the number of milliseconds from the epoch to the date value held in the object.