[ART]

Думаю, этих функций хватит:

Код:

unit Unit1;

interface

uses
  Windows,  Messages,  SysUtils,  Variants,  Classes,  Graphics,  Controls,  Forms, 
  Dialogs,  StdCtrls;

type
  TUser  =  record
   Password: string;
   Name: string;
  end;

type
  TForm1  =  class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R  * .dfm}

function User(N,  P: string): TUser;
begin
 Result.Name  :=  N;
 Result.Password  :=  P;
end;

procedure AddUser(User: TUser);
begin
 AssignFile(output,  'C:\Users.txt');
 Append(output);
  Writeln(User.Name);
  Writeln(User.Password);
 CloseFile(Output);
end;

function UserExists(User: TUser): boolean;
var
 P,  N: string;
begin
 AssignFile(input,  'C:\Users.txt');
 Reset(input);
 while not eof(input) do begin
  readln(N);
  readln(P);
  if (User.Name  =  N) and (User.Password  =  P) then begin
   Result  :=  true;
   CloseFile(input);
   exit;
  end;
 end;
Result  :=  false;
CloseFile(input);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
 if UserExists(User(Edit1.Text,  Edit2.Text))  =  false then Showmessage('Ты кто такой? Иди нафиг отсюда!') else Showmessage('Добро пожаловать!');
end;

end.