$str = <<<DEMO
<td class="f">
<a target="_blank" href="http://www.szonline.net/" onclick="return c(this.innerHTML,this.href,4,0,'77A717EA')">
</a>
<br/>
<font size="-1">
</font>
</td>
DEMO;

if (preg_match("/href=['\"]?(.*?)['\"]?\s+/is",$str,$m)) {
    echo $m[1];
}
else {
    echo "NO";
}