To load on old NTUser.dat, use the function LoadHive . You need to give the full name of the ntuser.dat file and the name of the registry key where to load the hive.

Code:
$filename = "c:\documents and settings\olduser\ntuser.dat"
$rootkey = "HKEY_USERS\olduser"
$ReturnCode = LoadHive( $rootkey, $filename)
If $ReturnCode = 0
  ? "Hive loaded...."

  $CitrixCheckVar = ReadValue ($rootkey+"\Software\SchnitzerCitrix", "2K3ProfileMigrateDone")
  IF $CitrixCheckVar = 1
    ? "This key exists, and therefore the ELSE Section has been done!";
  else
    ...
    ...
    $ReturnCode = Writevalue($rootkey+"\Software\SchnitzerCitrix","2K3ProfileMigrateDone","1","REG_SZ")

  endif

  $ReturnCode = UnLoadHive( $rootkey )
Endif
_________________________
Christophe