читайте
setTimeout/setInterval
<head>
<script type="text/javascript" src="http://code.jquery.com/jquery-1.9.1.min.js"></script>
</head><body>
<div id="elem">old text</div>
<script>
function textChange(change_text) {
$('#elem').animate({'opacity': 0}, 500, function() {
$('#elem').html(change_text) ;
$('#elem').animate({'opacity': 1}, 500, function() {
if(++i==arr.length) return ;
setTimeout(function() {
textChange(arr[i]) ;
}, 1000) ;
}) ;
}) ;
} ;
var i = 0 ;
var arr = ["new text1", "new text2", "new text3", "new text4"] ;
setTimeout(function() {textChange(arr[i]);}, 1000) ;
</script>
</body>