to write text over an image you may use absolute position for the text or the image, but i highly recommend to avoid that. instead of that, why dont you write the text below the image or somewhere else? then just use a mouse over event to change the display of the text, from none to inline or block.
<img src="image.gif" onMouseOver="display();" id="pic">
<span id="description" style="display: none;">text</span>
<script type="text/javascript">
function display(){document.getElementById("description").style.display="inline";}
</script>