function Roll()
{

    get = new Array("main_center","to","global");

for(arr = 0;arr < get.length; arr++){
ss = document.getElementById(get[arr]).getElementsByTagName("a");

		  for( i = 0;i < ss.length;i++ ){

				 ss[i].onmouseover = function(){
				 if( this.firstChild.tagName == "IMG" ){
				 this.firstChild.src = this.firstChild.src.replace("_off","_on" );
				 }
				 }

				 ss[i].onmouseout = function(){
				 if( this.firstChild.tagName == "IMG" ){
				 this.firstChild.src = this.firstChild.src.replace("_on","_off" );
				 }
				 }
	       
			}
		}
	 }