Код формы:
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object Form1: TForm1
  Left = 566
  Top = 225
  Width = 616
  Height = 79
  Caption = 'Form1'
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
  object Edit1: TEdit
    Left = 0
    Top = 0
    Width = 601
    Height = 21
    MaxLength = 20
    TabOrder = 0
    OnKeyUp = Edit1KeyUp //Это важно:)
  end
  object Edit2: TEdit
    Left = 0
    Top = 24
    Width = 553
    Height = 21
    Color = clMenu
    ReadOnly = True
    TabOrder = 1
  end
  object Edit3: TEdit
    Left = 560
    Top = 24
    Width = 41
    Height = 21
    AutoSize = False
    Color = clMenuBar
    ReadOnly = True
    TabOrder = 2
  end
end
===============
Код самой программы... Так сказать
-------------------------------
unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    Edit3: TEdit;
    procedure Edit1KeyUp(Sender: TObject; var Key: Word;
      Shift: TShiftState);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Edit1KeyUp(Sender: TObject; var Key: Word;
  Shift: TShiftState);
var
  s   : string;
  b, k: byte;
begin
  k := 0;
  s := Edit1.Text;
  while (pos('max', s) > 0) do
  begin
    b := pos('max', s);
    delete(s, b, 3);
    insert('min', s, b);
    inc(k);
  end;
  while (pos('макс', s) > 0) do
  begin
    b := pos('макс', s);
    delete(s, b, 4);
    insert('мин', s, b);
    inc(k);
  end;
  Edit3.Text := IntToStr(k);
  Edit2.Text := s;
end;
end.