Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

procedure MakeRounded(Control: TWinControl);
 var
   R: TRect;
   Rgn: HRGN;
 begin
   with Control do
   begin
     R := ClientRect;
     rgn := CreateRoundRectRgn(R.Left, R.Top, R.Right, R.Bottom, 20, 20);
     Perform(EM_GETRECT, 0, lParam(@r));
     InflateRect(r, - 5, - 5);
     Perform(EM_SETRECTNP, 0, lParam(@r));
     SetWindowRgn(Handle, rgn, True);
     Invalidate;
   end;
 end;


 procedure TForm1.Button1Click(Sender: TObject);
 begin
   // TMemo: 
  Memo1.BorderStyle := bsNone;
   MakeRounded(Memo1);
   // TEdit: 
  Edit2.BorderStyle := bsNone;
   MakeRounded(Edit2);
   // TPanel: 
  MakeRounded(Panel1);
   // TStaticText: 
  MakeRounded(StaticText1);
   // TForm 
  Form1.BorderStyle := bsNone;
   MakeRounded(Form1);
 end;