uses
 registry;
function IE_installed(var Version: string): Boolean;
var
 Reg: TRegistry;
begin
 Reg := TRegistry.Create;
 with Reg do
 begin
  RootKey := HKEY_LOCAL_MACHINE;
  OpenKey('Software\Microsoft\Internet Explorer', False);
  if ValueExists('Version') then
  Version := ReadString('Version')
  else
  Version := '';
  CloseKey;
  Free;
 end;
 Result := Version <> '';
end;
procedure TForm1.Button1Click(Sender: TObject);
var
 IE_Version: string;
begin
 if IE_Installed(IE_Version) then
  ShowMessage(Format('Internet Explorer %s installed.', [IE_Version]));
end;