How to pull data from complex array in php?

I am creating the post in the following form:

while ( $tracks = mysql_fetch_array($trackstring) ){
$tracks = mysql_fetch_array($trackstring) ){
echo "<li class="tracklist">
<input type="text" name="tracknum-[$tracks['song_id']]"
value="".$tracks['song_tracknumber']"/>
<input type="text" name="trackname[$tracks['song_id']]"
value="".$tracks['song_title'].""/>
</li>";
}

it's creating a $_POST array that looks like this:

Array ( [tracknum] => Array ( [13] => 1 [14] => 2 [15] => 3 ) [trackname] => Array ( [13] => One Beat [14] => Faraway [15] => Oh! )

essentially I want

1 - One Beat to go into id=13
2 - Faraway to go into id=14

I can see all the data there, but I'm not really sure how to manipulate it... I'm not so hot with arrays. How do I reference these with $_POST['????'] involving the id values