Date range picker using PHP&Javascript calendar

Hi guys.
I'm trying to pick 2 dates from a calendar on my webpage.
I've got 2 textboxes (date1 and date2) and the calendar image next to each of them which opens a separate window with the calendar.
It's all working fine, except for the fact that I can not seem to get the second date, even though I'm choosing it from the calendar. I'm not very skilled in Javascript, but I think the problem is within the insertdate() function and I don't know hoe to fix it.
I appreciate any help.

Here's the relevant pieces of code:

//mypage.php
...

...
echo"";
              echo"";
              echo "";
              echo"";
              echo"";
...
//scripts.js
function viewcalendar() {
  kalendarik = window.open("php_calendar/calendar.php", "kalendarik" , "location=0, menubar=0, scrollbars=0, status=0, titlebar=0, toolbar=0, directories=0, resizable=1, width=200, height=240, top=50, left=250");
  kalendarik.resizeTo(200, 240);
  kalendarik.moveTo(250, 50);
}

function insertdate(d) {
  window.close();
  window.opener.document.getElementById('date').value = d;

}

//calendar.php
include 'configure.php';
$month = isset($_GET['month'])? $_GET['month'] : date('n');
$pd = mktime (0,0,0,$month,1,date('Y'));// timestamp of the first day
$zd = -(date('w', $pd)? (date('w', $pd)-1) : 6)+1;// monday before
$kd = date('t', $pd);// last day of moth
echo '

      «
      '.$month_names[date('n', mktime(0,0,0,$month,1,date('Y')))].' '.date('Y', mktime(0,0,0,$month,1,date('Y'))).'
      »

    ';
for ($d=0;$d<7;$d++) {
  echo '
    '.$day_names[$d].'';
}
echo '
    ';
for ($d=$zd;$d<=$kd;$d++) {
  $i = mktime (0,0,0,$month,$d,date('Y'));
  if ($i >= $pd) {
    $today = (date('Ymd') == date('Ymd', $i))? '_today' : '';
    $minulost = (date('Ymd') >= date('Ymd', $i+86400)) && !$allow_past;
    echo '
    '.($minulost? date('j', $i) : ''.date('j', $i).'').'';

  } else {
    echo '
     ';
  }
  if (date('w', $i) == 0 && $i >= $pd) {
    echo '
    ';
  }
}

I've still didn't figure it out, so any suggestion would be helpful... thank you.

[JRM]

function insertdate(d) {
window.close();
window.opener.document.getElementById('date').value = d;

You are right about this being the issue.
This code is only going to fill the value of a single date element.
If you have two date elements, then it has to be an array.

function insertdate(d) {
window.close();
window.opener.document.getElementById('date').value = d;

You are right about this being the issue.
This code is only going to fill the value of a single date element.
If you have two date elements, then it has to be an array.

So you're saying I should have something like that:

function insertdate(d) {
window.close();
window.opener.document.getElementById('date1').value = d[0];
window.close();
window.opener.document.getElementById('date2').value = d[1];
}

But then how do I adapt the PHP code which sets the 2 dates and calls the insertdate function?

[JRM]

I don't know if both dates will be there or not. It depends on how that part of the code is.
Maybe the simplest approach is to do one at a time, but they STILL need to be differentiated from each other somehow, like date1 date2 or date[].
If the output of the calender is d , call it for each field and drop it into value.
Those element exist, (via hard coding ,PHP echo, or js DOM.) so when the value is populated by d PHP will pick them up as
$_POST[date1], $_POST[date2]

function insertdate(d) {
window.close();
window.opener.document.getElementById('date1').value = d[0];
window.close();
window.opener.document.getElementById('date2').value = d[1];
}

I did not manage to make it work, so I replaced the calendars with drop down lists for dates which work just fine.