This works for me.....

Code
<script language=JavaScript>
var ad=new Array()
ad[0]='http://www.mysite.com/banners/1.gif';
ad[1]='http://www.mysite.com/banners/2.gif';
ad[2]='http://www.mysite.com/banners/3.gif';

var links=new Array()
links[0]='http://www.1_site.com';
links[1]='http://www.2_site.com';
links[2]='http://www.3_site.com';

var xy=Math.floor(Math.random()*ad.length);
document.write('<a href="'+links[xy]+'" target="_self"><img src="'+ad[xy]+'" width="468" height="60" border="0" alt="Click here"></a>');
</script>


Just drop it in where you want the banner to be.
Of course visitors will need javascript enabled - so you may want to consider a php option. smile