banner rotation script

I am trying to get this banner rotation script to work but all I am seeing
are totally blank lines:

<?
$bannerCounter =1;

$bannerCode[$bannerCounter] = "<a href=\"http://www.example.com/site1\";
target=\"_top"><iframe src=\"http://www.example.com/site1\";
marginwidth=\"0\" marginheight=\"0\" width=\"120\" height=\"150\" border="0"
frameborder="0" style="border:none;" scrolling="no"> </iframe></a>\";
$bannerCounter++;

$bannerCode[$bannerCounter] = "<a href=\"http://www.example.com/site2\";
target=\"_top\"><img src=\"http://www.example.com/site2\"; width=\"120\"
height=\"600\" alt=\"null\" border=\"0\"/></a> ";
$bannerCounter++;

$bannerCode[$bannerCounter] = "<a href=\"http://www.example.com/site3\";
target=\"_top\"><img src=\"www.example.com/site3\" width=\"468\"
height=\"60\" alt=\"site 3\" border=\"0\"/></a>";
$bannerCounter++;

$bannerCode[$bannerCounter] = "<a href=\"<a
href=\"http://www.example.com/site4\"; target=\"_top\"><img
src=\"http://www.example.com/site4\"; width=\"600\" height=\"500\"
alt=\"null\" border=\"0\"/></a>";
$bannerCounter++;





$bannerAdTotals = $bannerCounter - 1;
if($bannerAdTotals>1)
{
mt_srand((double)microtime() * 1234567);
$bannerPicked = mt_rand(1, $bannerAdTotals);
}
else
{
$bannerPicked = 1;
}
$bannerAd = $bannerCode[$bannerPicked];
?>
$bannerAd = str_replace('"', '\'', $bannerAd);
print("document.write(\"$bannerAd\")");



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