$area = array("北海道", "青森", "秋田", "......略 "沖縄");
$select = "<select name='area'>";
for ($i = 0; $i < 47; $i++) {
$select .= "<option value='$i'>$area[$i];
}
$select .= "</select>";


受け取る側
$num = $_POST['area'];
echo "<script language='javascript' charset='euc-jp' type='text/javascript' src='http://weather.livedoor.com/plugin/common/forecast/$i.js'>;</script>";

とか？