Banner Javascript

I have a program to rotate banners called bannermaster and to rotate banner in other sites I have to use the following script:

<script language="JavaScript">
<!-- Hide the script from old browsers --

// CHANGE THESE 3 Variables for yourself

var click = "http://internet/cgi-bin/click.cgi";
var bms = "http://internet/cgi-bin/bms.cgi";
var bm = "http://internet/cgi-bin/bm.cgi";

// LEAVE THE REST ALONE


var axel = Math.random() + ""
var rand1 = axel.charAt(5)
var rand2 = (axel.charAt(6) == "0") ? "1" : axel.charAt(6)
var random = rand1 + rand2 + ""
var bN = navigator.appName;
var bV = parseInt(navigator.appVersion);
var agt = navigator.userAgent.toLowerCase();


if (bN=='Netscape') {
var banner = '<a href="' + click + '?x-factor=' + random + '">' +
'<img src="' + bms + '?x-factor=' + random + '" border=0></a>';
}

if (bN=='Microsoft Internet Explorer') {
var banner = '<ifr'+'ame id=IBG src="' + bm + '" width=468 height=73' +
'marginwidth=0 marginheight=0 hspace=0 vspace=0 ' +
'frameborder=0 scrolling=no></ifr'+'ame>';
}

document.write(banner);

//--End Hiding Here -->
</script>

The script works fine in IE but in Netscape I can just click once in the same banner.

Can anyone knows how to correct this script!?

Thanks

Rui