var banner = new Array();

banner[0]='http://i18.servimg.com/u/f18/14/18/56/91/header23.png';
banner[1]='http://i18.servimg.com/u/f18/14/18/56/91/header24.png';
banner[2]='http://i18.servimg.com/u/f18/14/18/56/91/header25.png';
banner[3]='http://i18.servimg.com/u/f18/14/18/56/91/header26.png';
banner[4]='http://i18.servimg.com/u/f18/14/18/56/91/header27.png';
banner[5]='http://i18.servimg.com/u/f18/14/18/56/91/header28.png';
banner[6]='http://i18.servimg.com/u/f18/14/18/56/91/header29.png';

document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];