// JavaScript Multiple Rollover
function rollover(imgID) {
  // get the image object we're referring to
  var thisimg = document.getElementById(imgID);
  // and add "_on" to its src
  thisimg.src = thisimg.src.replace(/(\.[a-z0-9]+)$/i,'_on$1');
}
function rollout(imgID) {
  // get the image object we're referring to
  var thisimg = document.getElementById(imgID);
  // and remove "_on" from its src
  thisimg.src = thisimg.src.replace(/_on(\.[a-z0-9]+)$/i,'$1');
}
/* 
	Add to html
<img src="roll.gif" id="roll"
     onmouseover="rollover('roll')"
     onmouseout="rollout('roll')">
<img src="roll2.gif" id="roll2"
     onmouseover="rollover('roll2')"
     onmouseout="rollout('roll2')">
*/