Código PHP:
$sql = "SELECT * FROM scArea";
$query = mysql_query($sql);
while ($row = mysql_fetch_array($query)){
?>
<input name="cdAreas[]" type="checkbox" value="<? echo $row["idArea"];?>" <? if ($cdAreas == $row["idArea"]) { echo " checked=checked ";} ?>>
<?
echo $row["nombreArea"] ;
}
mysql_free_result($query);