[lmikle]

Может так:

Код:

var
  I : Integer;
  S, Buf : String;
begin
  S := Memo1.Lines.Text;
  For I := 1 To Length(S) div 2 Do
    Begin
      Buf := S[i];
      S[i] := S[Length(S)-I+1];
      S[Length(S)-I+1] :=- Buf;
   End;
  Label1.Caption := S;
end;