...change a user's password for a specified network server or domain ?

function NetUserChangePassword(Domain: PWideChar; UserName: PWideChar; OldPassword: PWideChar;
  NewPassword: PWideChar): Longint; stdcall; external 'netapi32.dll'
  Name 'NetUserChangePassword';

// Changes a user's password for a specified network server or domain.
// Requirements:  Windows NT/2000/XP
// Windows 95/98/Me: You can use the PwdChangePassword function to change a user's
// Windows logon password on these platforms

procedure TForm1.Button1Click(Sender: TObject);
begin
  NetUserChangePassword(PWideChar(WideString('\\COMPUTER')),
    PWideChar(WideString('username')),
    PWideChar(WideString('oldpass')),
    PWideChar(WideString('newpass')));
end;