Use this procedure to hide (AVisible=True) or show (AVisible=False) the start button:

procedure TForm1.HideStartButton(AVisible: Boolean);
var
  Tray,Child,StartButtonHandle: HWnd;
  C: array[0..127] of Char;
  S: string;
begin
  Tray:=FindWindow('Shell_TrayWnd',nil);
  Child:=GetWindow(Tray,GW_CHILD);
  while Child<>0 do
  begin
    if GetClassName(Child,C,SizeOf(C))>0 then
    begin
      S:=StrPas(C);
      if UpperCase(S)='BUTTON' then
      begin
        StartButtonHandle:=Child;
        if AVisible then ShowWindow(Child,1)
        else ShowWindow(Child,0);
      end;
    end;
    Child:=GetWindow(Child,GW_HWNDNEXT);
  end;
end;

First of all, you should find handle of the window, which are the desktop. And after that, you may work with it like with any other window.

// Hide icons on the Desktop
procedure TForm1.Button2Click(Sender: TObject);
begin
  ShowWindow(DesktopListViewHandle, SW_HIDE);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  DesktopListViewHandle:=FindWindow('ProgMan', nil);
  DesktopListViewHandle:=GetWindow(DesktopListViewHandle, GW_CHILD);
  DesktopListViewHandle:=GetWindow(DesktopListViewHandle, GW_CHILD);
end;

// Show icons on the Desktop
procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowWindow(DesktopListViewHandle, SW_SHOW);
end;

Information about CD autorun is stored in the registry at "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\CDROM\AutoRun" path. If this parameter is 0, then autorun is disabled, if this parameter is 1, then autorun is enabled. Don't forget to add Registry in the uses chapter.

uses
  Registry;
...
procedure TForm1.Button1Click(Sender: TObject);
var
  i: Boolean;
begin
  i:=False;
  with TRegistry.Create do
  begin
    RootKey:=HKEY_LOCAL_MACHINE;
    if KeyExists('System\CurrentControlSet\Services\Class\CDROM')and
       OpenKey(
         'System\CurrentControlSet\Services\Class\CDROM', 
         False) then
      WriteBinaryData('AutoRun', i, 1);
  end;
end;

Taskbar window name is 'Shell_TrayWnd'. Use FindWindow function to find Taskbar handle, and EnableWindow function to disable/enable taskbar. For example:

var
  TaskbarHandle: THandle;
...

procedure TForm1.FormCreate(Sender: TObject);
begin
  TaskbarHandle:=FindWindow('Shell_TrayWnd', nil);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  EnableWindow(TaskbarHandle, False);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  EnableWindow(TaskbarHandle, True);
end;