uploadfile con Ajax

[chricas]

Gracias he decidido utilizar swfupload funciona pero no de la manera que quiero, necesito crear una carpeta donde almacenar archivos, a veces la crea y guarda el archivo con el nombre que le ordeno pero al querer guardar otro archivo en la misma carpeta lo hace pero en la raiz de mi sitio... pego el codigo que tengo en espera que alguno d ustedes me pueda colaborar:

// Code for Session Cookie workaround
if (isset($_POST["PHPSESSID"])) {
session_id($_POST["PHPSESSID"]);
} else if (isset($_GET["PHPSESSID"])) {
session_id($_GET["PHPSESSID"]);
}

session_start();

// Check post_max_size (http://us3.php.net/manual/en/features.file-upload.php#73762)
$POST_MAX_SIZE = ini_get('post_max_size');
$unit = strtoupper(substr($POST_MAX_SIZE, -1));
$multiplier = ($unit == 'M' ? 1048576 : ($unit == 'K' ? 1024 : ($unit == 'G' ? 1073741824 : 1)));

if ((int)$_SERVER['CONTENT_LENGTH'] > $multiplier*(int)$POST_MAX_SIZE && $POST_MAX_SIZE) {
header("HTTP/1.1 500 Internal Server Error"); // This will trigger an uploadError event in SWFUpload
echo "POST exceeded maximum allowed size.";
exit(0);
}

// Settings

//Condicion para ver si llega el nombre de la carpeta y el archivo donde y con que almacenar
if(isset($_POST["carpeta"]) $$ isset($_POST["nombre"]))
{
$carpeta = $_POST["carpeta"];
$nombre = $_POST["nombre"];
if(!is_dir("uploads/$carpeta/")) //Si no existe la carpeta la creo
{
if (!mkdir( "uploads/$carpeta/", 0777))
$save_path = "uploads/";
else
// The path were we will save the file (getcwd() may not be reliable and should be tested in your environment)
$save_path = "uploads/$carpeta/";
}
else
$save_path = "uploads/$carpeta/";

}

$upload_name = "Filedata";
$max_file_size_in_bytes = 2147483647; // 2GB in bytes
$extension_whitelist = array("pdf", "jpg", "gif", "png"); // Allowed file extensions
$valid_chars_regex = '.A-Z0-9_ !@#$%^&()+={}\[\]\',~`-'; // Characters allowed in the file name (in a Regular Expression format)

// Other variables
$MAX_FILENAME_LENGTH = 260;
$file_name = "";
$file_extension = "";
$uploadErrors = array(
0=>"There is no error, the file uploaded with success",
1=>"The uploaded file exceeds the upload_max_filesize directive in php.ini",
2=>"The uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form",
3=>"The uploaded file was only partially uploaded",
4=>"No file was uploaded",
6=>"Missing a temporary folder"
);

// Validate the upload
if (!isset($_FILES[$upload_name])) {
HandleError("No upload found in \$_FILES for " . $upload_name);
exit(0);
} else if (isset($_FILES[$upload_name]["error"]) && $_FILES[$upload_name]["error"] != 0) {
HandleError($uploadErrors[$_FILES[$upload_name]["error"]]);
exit(0);
} else if (!isset($_FILES[$upload_name]["tmp_name"]) || !@is_uploaded_file($_FILES[$upload_name]["tmp_name"])) {
HandleError("Upload failed is_uploaded_file test.");
exit(0);
} else if (!isset($_FILES[$upload_name]['name'])) {
HandleError("File has no name.");
exit(0);
}

// Validate the file size (Warning: the largest files supported by this code is 2GB)
$file_size = @filesize($_FILES[$upload_name]["tmp_name"]);
if (!$file_size || $file_size > $max_file_size_in_bytes) {
HandleError("File exceeds the maximum allowed size");
exit(0);
}

if ($file_size <= 0) {
HandleError("File size outside allowed lower bound");
exit(0);
}

// Validate file name (for our purposes we'll just remove invalid characters)
$file_name = preg_replace('/[^'.$valid_chars_regex.']|\.+$/i', "", basename($_FILES[$upload_name]['name']));
if (strlen($file_name) == 0 || strlen($file_name) > $MAX_FILENAME_LENGTH) {
HandleError("Invalid file name");
exit(0);
}

// Validate that we won't over-write an existing file
if (file_exists($save_path . $file_name)) {
HandleError("File with this name already exists");
exit(0);
}

// Validate file extension
$path_info = pathinfo($_FILES[$upload_name]['name']);
$file_extension = $path_info["extension"];
$is_valid_extension = false;
foreach ($extension_whitelist as $extension) {
if (strcasecmp($file_extension, $extension) == 0) {
$is_valid_extension = true;
break;
}
}
if (!$is_valid_extension) {
HandleError("Invalid file extension");
exit(0);
}

if(!isset($carpeta)
$save_path = "uploads/";
if(!isset($nombre)
$nombre = $filename;


//Aqui guardo el archivo
if (!@move_uploaded_file($_FILES[$upload_name]["tmp_name"], $save_path.$nombre.".".$file_extension/)) {
HandleError("File could not be saved.");
exit(0);
}

exit(0);

/* Handles the error output. This error message will be sent to the uploadSuccess event handler. The event handler
will have to check for any error messages and react as needed. */
function HandleError($message) {
echo $message;
}