img = new Array(3); 
img[0] = "<img src=http://emulex.pl/next/1.jpg border=0>";
img[1] = "<img src=http://emulex.pl/next/2.jpg border=0>";
img[2] = "<img src=http://emulex.pl/next/3.jpg border=0>";

index = Math.floor(Math.random() * img.length);
document.write( img[index] );