public function myform(){
   ...
   $fields->insertBefore($att=new FileField("Attachments[]", "Attachments"), "Title");
   $att->setFolderName('fileattachments');
   ...
}

public function project_save($data, $form){
   ...
      // save file attachments into record;
      $i = 0;
      while(isset($data['Attachments']['tmp_name'][$i])) {
         if (!empty($data['Attachments']['name'][$i])) {
            // create new single file array from file uploads array
            $file = array();
            $file['name'] = $data['Attachments']['name'][$i];
            $file['type'] = $data['Attachments']['type'][$i];
            $file['tmp_name'] = $data['Attachments']['tmp_name'][$i];
            $file['error'] = $data['Attachments']['error'][$i];
            $file['size'] = $data['Attachments']['size'][$i];
            
            // create & write uploaded file in DB
            try {
               $fileClass = File::get_class_for_file_extension(pathinfo($file['name'], PATHINFO_EXTENSION));
               $newfile = new $fileClass();
               $upload = new Upload();
               // get folder from form upload field
               $folder = $form->Fields()->fieldByName('Attachments[]')->getFolderName();
               $folderObj = Folder::find_or_make($folder);
               $upload->loadIntoFile($file, $newfile, $folder);
               $fileObj = $upload->getFile();
               // for some reason the Filename is off...
//               $fileObj->setFilename( "assets/$folder/".$fileObj->Name );
//               $fileObj->setParentID( $folderObj->ID );
//               $fileObj->write();
               $this->Record->Attachments()->add($fileObj);
            } catch(ValidationException $e) {
               $form->sessionMessage('Extension not allowed...','bad');
               return $this->redirectBack();
            }
         }
         $i++;
      }
      $this->Record->write();
   ...
}

$upload->loadIntoFile($file, $newfile, $folder);
$fileObj = $upload->getFile();