And the code to do this:

function selectText() {
	this.focus();
	this.select();
}

function IEselectText(element) {
	element.focus();
	element.select();
}

function setEvents() {
	if (document.getElementsByTagName('textarea')) {
		var textareas = document.getElementsByTagName('textarea');
		for (var i=0;i<textareas.length;i++) {
			try { textareas[i].addEventListener('click', selectText, false); }
			catch(e) {
				textareas[i].attachEvent('onclick',function () { IEselectText(event.srcElement); 
				});
	  		}
		}
	}
}


window.onload = setEvents;