Как-то так:
<script type="text/javascript">
var i=1;
var text=new Array(5);
text[0]='Text1';
text[1]='Text2';
text[2]='Text3';
text[3]='Text4';
text[4]='Text5';
function change_text()
{
document.getElementById('text_change').innerHTML = text[i];
i++; if(i==5) i=0;
}
</script>
<span id="text_change" onmouseover="change_text()">Text1</span>