Someone

function populate_genre(s, id)
{
	// 's' should be a reference to 'idParentGenre' select node

	if (s.options[s.selectedIndex].value == "")
		return;
	
	ajax.open("post", "inc/ajax/_getGenres.php", true);
	ajax.send("idParent="+ s.options[s.selectedIndex].value);
    
	var f_s = document.getElementById("idGenre");					// should be only 1
	f_s.options.length = 0;
	f_s.options[0] = new Option("Loading Music Genres For "+ s.options[s.selectedIndex].text +"....", null);
	
	if (id != undefined)
		ajax.idGenre = id;
	
	ajax.onSuccess = function()
	{
		var i, len;
		var arr = eval(this.data);
		var f_s = document.getElementById("idGenre");
		
		f_s.options.length = 0;
		
		len = arr.length;
		for (i = 0; i < len; i++)
		{
			f_s.options[i] = new Option(arr[i].name, arr[i].id);
			if (this.idFormat != undefined && arr[i].id == this.idFormat)
				f_s.options[i].selected = true;
		}
		
		if (this.idGenre != undefined)
			this.idGenre = undefined;
		else
			f_s.focus();				// only focus the field if we're not reseting the form
	}
}