AJAX - probleme envoi d'un POST

echo "<A href='#' onclick='supp(".$ID.");'>Supprimer</A>

function supp(Var1)
{
  var xhr = GetXHR();
  xhr.onreadystatechange = function()
  {
    if(xhr.readyState == 4 && xhr.status == 200)
    {
      leselect = xhr.responseText;
      document.getElementById('suppDIV').innerHTML = leselect;
    }
  }
  url = "/html/requete-ajax.php";
  xhr.open("POST",url,false);
  
  alert(Var1);
  xhr.send('idphoto=' + 'Var1');
}

if( isset( $_POST['idphoto'] ) )

<A href='gestion_photos.php?id=".$ID."'>Supprimer</A>

if (isset( $_POST['idphoto'] ))
{
	echo "OK";
}
else
{
	echo "NAN";
}

function supp(Var1)
{
  var xhr = GetXHR();
  url = "/html/requete-ajax.php";
  xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
  xhr.open("POST",url,false);
  alert(Var1);
  xhr.send('idphoto=' + Var1);
}

function supp(Var1)
{
  var xhr = GetXHR();
  url = "/html/requete-ajax.php";
  xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
  xhr.open("POST",url,true);
  xhr.send('idphoto=' + Var1);
  alert(Var1);
}code]

Et donc dans ma page "requete-ajax.php" j'ai juste mis en haut de page : 
[code=php]if( isset( $_GET['idphoto'] ) && $_GET['idphoto'] != "" )
{
	echo "OUAIIIIIIIIIIIIIIIIIIIIIIIIIIS";
}
else
{
	echo "NAAAAAAAAAAAAAAAAAAAAAAAAAAN";
}

alert("Etat de la requête : "+xhr.readyState);

if( isset( $_POST['idphoto'] ) && $_POST['idphoto'] != "" )
{
  echo "OUAIIIIIIIIIIIIIIIIIIIIIIIIIIS";
}
else
{
  echo "NAAAAAAAAAAAAAAAAAAAAAAAAAAN";
}

function supp(Var1)
{
  var xhr = GetXHR();
  xhr.onreadystatechange = function()
  {
    if(xhr.readyState == 4 && xhr.status == 200)
    {
      leselect = xhr.responseText;
      document.getElementById('suppDIV').innerHTML = leselect;
    }
  }
  url = "/html/requete-ajax.php";
  xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
  xhr.open("POST",url,false);
  xhr.send('idphoto=' + Var1);
  alert("Etat de la requête : " + xhr.readyState);
}

xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");

function GetXHR()
{
  var xhr = null; 

  if(window.XMLHttpRequest)
  {
    xhr = new XMLHttpRequest();
  }
  else if(window.ActiveXObject)
  {
    try
    {
      xhr = new ActiveXObject("Msxml2.XMLHTTP");
    }
    catch (e)
    {
      xhr = new ActiveXObject("Microsoft.XMLHTTP");
    }
  }
  else
  {
    alert("Votre navigateur ne supporte pas l\'ajax..."); 
    xhr = false; 
  }
  return xhr;
}