function get_random()
{
    var ranNum= Math.floor(Math.random()*3);
    return ranNum;
}


   var whichImage=get_random();

    var image=new Array(2)
     image[0]='<img src="img/index_r1_c1.jpg"  border="0"/>';
     image[1]='<img src="img/index_r1_c1a.jpg"  border="0"/>';
     image[2]='<img src="img/index_r1_c1c.jpg"  border="0"/>'; 
	 image[3]='<img src="img/index_r1_c1d.jpg"  border="0"/>';
     image[4]='<img src="img/index_r1_c1e.jpg"  border="0"/>';
     
  
   document.write(image[whichImage]);