You can simply add a redirect in the index page to the registration page

if(!isloggedin()){

forward('pg/register');

}

If you are looking for registration form in index page, you can call the registration form by including the elgg view for it in the index page

echo elgg_view('account/forms/register');

Thanks Team Webgalli I did just that and it works!!!

You came to save the day I see you responded to a lot of questions!!! lol