pics=new Array; 

pics[1]="images/left_pix.jpg"; 

pics[2]="images/left_pix1.jpg";  

pics[3]="images/left_pix2.jpg";  

function ShowPix() {

num = Math.random();
num = 1 + ( num * ((pics.length - 1)-1));
num = Math.round(num);

document.write("<img src='" + pics[num] + "' border='0' ");
}