var banner = new Array();

banner[0]='http://lh3.ggpht.com/_X0OjV6jPtlk/S4kyqWXoVHI/AAAAAAAAB2A/hP_FD0UF9JM/Banner%20V3.png';
banner[1]='http://lh3.ggpht.com/_X0OjV6jPtlk/S4kyqbHMWiI/AAAAAAAAB2E/UIvX7mvHFjM/Banner%20V4.png';
banner[2]='http://lh3.ggpht.com/_X0OjV6jPtlk/S4khBYIoLfI/AAAAAAAAB14/RBrZrbfejtk/Banner%20V2.png';

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