Think i got it:
<?php
$ad = "<div class="image-advertisement" id="ad-306"><a href="http://www.appraisalbuzz.com/ad/redirect/306/0" onclick="window.open(this.href); return false;"><img src="http://appraisalbuzz.com/sites/default/files/FREA_BannerWebinarBrianT.gif" alt="" title="" width="468" height="60" /></a></div><div class="links-to">Links to http://www.frea.com/</div>";
$pattern = array();
$pattern[0] = '/<div class="image-advertisement" id="ad-[0-9]+">/';
$pattern[1] = '/<\/div><div class="links-to">Links to (http|ftp|https):\/\/[\w\-_]+(\.[\w\-_]+)+([\w\-\.,@?^=%&:\/~\+#]*[\w\-\@?^=%&\/~\+#])?+/';
$replace = array();
$replace[0] = '';
$replace[1] = '';
echo preg_replace($pattern, $replace, $ad);
?>