img = new Array(4); 
img[0] = "<img src=http://www.wydawnictwortw.pl/kds_sklep/rotator/banery/baner1.jpg alt='www.ksiazkidosluchania.pl' width=500 height=220 border=0>";
img[1] = "<img src=http://www.wydawnictwortw.pl/kds_sklep/rotator/banery/baner1.jpg alt='www.ksiazkidosluchania.pl' width=500 height=220 border=0>";
img[2] = "<img src=http://www.wydawnictwortw.pl/kds_sklep/rotator/banery/baner1.jpg alt='www.ksiazkidosluchania.pl' width=500 height=220 border=0>";
img[3] = "<img src=http://www.wydawnictwortw.pl/kds_sklep/rotator/banery/baner1.jpg alt='www.ksiazkidosluchania.pl' width=500 height=220 border=0>";
index = Math.floor(Math.random() * img.length);
document.write( img[index] );