// Define advertising tags
var bottom_ads = [
   [ '<a href="http://www.nvp.cz/" ><img alt="Nebe v plamenech - nejlepší akce na mobilu" src="/images/mm/banners/nvp_420x60a_2.gif" border="0" width="420" height="60"></a>' ],
   [ '<a href="http://www.nvp.cz/" ><img alt="Nebe v plamenech - nejlepší akce na mobilu" src="/images/mm/banners/nvpbanner.jpg" border="0" width="468" height="60"></a>' ]
];

// Choose random adv tag
var bottom_adindex = Math.round( Math.random() * (bottom_ads.length-1) );

// Write it to document
document.write(bottom_ads[bottom_adindex]);