protectedfor, не совсем на регулярках:
$str = <<<HTML
<table>
<tr><td></td></tr>
</table>
<table>
<tr style="height:25px">
<td>1231</td><td>dsaa</td><td></td><td></td>
</tr>
<tr style="height:25px">
<td>1231</td><td>ddsaa</td><td></td><td></td>
</tr>
<tr style="height:25px">
<td>1231</td><td>dsaa</td><td></td><td></td>
</tr>
</table><table></table>
HTML;
$m = array();
preg_match_all("/(<tr[^>]+?height:25px.*?<\/tr>)/", str_replace("\n", "", $str), $m);
$m = array_map(function($v) {
return new SimpleXMLElement($v);
}, $m[1]);
echo $m[0]->td[0], "\n";
echo $m[0]->td[1], "\n";
echo $m[1]->td[0], "\n";
echo $m[1]->td[1], "\n";