Any reason why you're escaping all your quotes instead of using PHP heredocs?
They make it much easier to paste code in without having to escape everything.
PHP Code:
$output.=<<<OUTPUT
<div align="center" style="padding:4px;overflow:hidden;">
<script type="text/javascript"><!--
google_ad_client = "pub-CODE;
google_ad_width = 728;
google_ad_height = 90;
google_ad_format = "728x90_as";
google_ad_type = "text_image";
google_ad_channel ="123456789";
google_color_border = "336699";
google_color_bg = "FFFFFF";
google_color_link = "0000FF";
google_color_text = "000000";
google_color_url = "008000";
//--></script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
</div>
<table width="100%" border="0" cellpadding="4" cellspacing="0">
<tr><td width="85%" valign="top">
OUTPUT;
Unless there's some negative to using that method I'm not aware of?