Here is an example:
HTML code:
<img id="myImg" src="http://static.jquery.com/files/rocker/images/logo_jquery_215x53.gif"/>
JavaScript code:
$(document).ready(function() {
$( "#myImg" ).mouseover(function(){
$(this).attr("src", "http://www.jqueryui.com/images/logo.gif");
});
$( "#myImg" ).mouseout(function(){
$(this).attr("src", "http://static.jquery.com/files/rocker/images/logo_jquery_215x53.gif");
});
});
Edit: Sorry, your code was a bit strange. Now I understood what you were doing. ;) The hover method is better, of course.
<a href="" onMouseOver="document.MyImage.src='http://icons.iconarchive.com/icons/uiconstock/round-edge-social/72/ask-icon.png';" onMouseOut="document.MyImage.src='http://icons.iconarchive.com/icons/uiconstock/round-edge-social/72/arto-icon.png';">
<img src="http://icons.iconarchive.com/icons/uiconstock/round-edge-social/72/arto-icon.png" name="MyImage">
Demo http://jsfiddle.net/W6zs5/