hola ajalex,
de esta forma tu script deberia funcionar
Código PHP:
<?php
include "config.php";
$sql = "SELECT * FROM plans where prin='1' limit 0,10" ;
$resp = mysql_query($sql);
$par = 0;
echo "<table width=100% border=1>";
while($plan = mysql_fetch_array($resp)) {
if ($par % 3 == 0)
echo "<tr valign=\"top\"><td>";
?>
Aqui
<?
if ($par % 3 == 0)
echo "</td><td>";
else
echo "</td></tr>";
$par++;
}
echo "</table>";
?>