PHP Code:
<script language="JavaScript">
url = new Array;
url[0] = 'http://www.address1.pl';
url[1] = 'http://www.address2.pl';
url[2] = 'http://www.address3.pl';
desc = new Array;
desc[0] = 'Description 1';
desc[1] = 'Description 2';
desc[2] = 'Description 3';
ads = Math.floor(Math.random()*url.length);
document.write('<a href="' + url[ads] + '" target="_blank"><img src="banner' + ads + '.gif" border="0" alt="' + desc[ads] + '"><br>' + desc[ads] + '</a>');
</script>
put this script just in place where you want to show random banners
name the files banner1.gif, banner2.gif, banner3.gif, etc.
you may use this script only once within the one .html file