もう、おまけで、ボタンもつけちゃうんだから。!!
この、もってけ泥棒さん。!!

<html>
<head>
<title>PHP TEST</title>

</head>
<body>
    <form method="POST" action="calendar.php" style="color:#000000; border:1px solid #ccc; float: left;">
        <input type="submit" value="<<">
<?
    if ( $_POST["NENTUKIHIGW"] ) {
        $NENPW = substr($_POST["NENTUKIHIGW"], 0, 4) ;
        $TSUKIPW = substr($_POST["NENTUKIHIGW"], 4, 2) ;
        $NENTSUKIHIPW = date("Ymd",mktime(0,0,0, $TSUKIPW - 1, 1,$NENPW));
    } else {
        $NENTSUKIHIPW = date("Ymd",mktime(0,0,0, date("m")-1, 1, date("Y")));
    }
    echo "<input type='hidden' name='NENTUKIHIGW' value='$NENTSUKIHIPW'>\n"
?>
    </form>
<?
    if ( $_POST["NENTUKIHIGW"] ) {
        $NENPW = substr($_POST["NENTUKIHIGW"], 0, 4) ;
        $TSUKIPW = substr($_POST["NENTUKIHIGW"], 4, 2) ;
    } else {
        $NENPW = date("Y");
        $TSUKIPW = date("m");
    }
    echo "<div style='color:#000000; border:1px solid #ccc; float: left;'>".$NENPW."".$TSUKIPW." 月 </div>\n";
?>
    <form method="POST" action="calendar.php" style="color:#000000; border:1px solid #ccc; float: left;">
        <input type="submit" value=">>">
<?
    if ( $_POST["NENTUKIHIGW"] ) {
        $NENPW = substr($_POST["NENTUKIHIGW"], 0, 4) ;
        $TSUKIPW = substr($_POST["NENTUKIHIGW"], 4, 2) ;
        $NENTSUKIHIPW = date("Ymd",mktime(0,0,0, $TSUKIPW + 1, 1,$NENPW));
    } else {
        $NENTSUKIHIPW = date("Ymd",mktime(0,0,0, date("m")+1, 1, date("Y")));
    }
    echo "<input type='hidden' name='NENTUKIHIGW' value='$NENTSUKIHIPW'>\n";
?>
    </form>
    <br>
    <br>
    <br>
<?php
///usr/share/php/smarty/Smarty.class.php
if ( $_POST["NENTUKIHIGW"] ) {
    $NENPW = substr($_POST["NENTUKIHIGW"], 0, 4) ;
    $TSUKIPW = substr($_POST["NENTUKIHIGW"], 4, 2) ;
    $HISUPW = date("d",mktime(0, 0, 0, $TSUKIPW + 1, 0, $NENPW ));
} else {
    $NENPW = date("Y");
    $TSUKIPW = date("m"); 
    $HISUPW = date("d",mktime(0, 0, 0, $TSUKIPW + 1, 0, $NENPW ));
}
$IPW = 1;
while ($IPW <= $HISUPW){
    $TSPW = mktime(0, 0, 0, $TSUKIPW, $IPW, $NENPW );
    $YOUBIPW = date("w",$TSPW);
    if ( $YOUBIPW == 0 ){
        print('<div style="color:#ff0000; border:1px solid #ccc; width: 20px; float: left;">'.$IPW."</div>\n");  
    }elseif( $YOUBIPW == 6 ){
        print('<div style="color:#0000ff; border:1px solid #ccc; width: 20px; float: left;">'.$IPW."</div>\n");
    }else{
        print('<div style="color:#000000; border:1px solid #ccc; width: 20px; float: left;">'.$IPW."</div>\n");
    }
    ++$IPW;
}
?>
</body>
</html>