function RemoveClassName(objElement, strClass) {
	if (objElement.className) {
		var arrList = objElement.className.split(' ');
		var strClassUpper = strClass.toUpperCase();
		for ( var i = 0; i < arrList.length; i++ ) {
			if ( arrList[i].toUpperCase() == strClassUpper ) {
				arrList.splice(i, 1);
				i--;
			}
		}
		objElement.className = arrList.join(' ');
	}
}

var trs = document.getElementById("playlist").getElementsByTagName("tr");

for (var i = 0; i < trs.length; i++) {
	trs[i].onmousedown = function() {
		for (var j = 0; j < trs.length; j++) {
			RemoveClassName(trs[j], "selected")
		}
		this.className += " selected";
	}
}