Prevent/Restrict access to website until offical launch?

Is there a way that I can password proctect or only allowing certain ip's to the whole site before the offical launch?

I usually just add an index.html page (which overrides the index.php) to the root of the site until the site is ready. however if you already have had spiders on the site this will not stop it being indexed and discoverable in the search engines.

Create, or modify, the .htaccess file in the store's root directory (where the index.php and ipn_main_handler.php reside), adding the following towards the top of the file:

Order Deny,Allow
Deny from all
Allow from 100.100.100.100
Allow from 200.200.200.200

Of course, you'll be specifying the IP addresses that you want to have access instead of the example values! Depending on your payment methods, you might have to add an IP address or range to allow the post-backs to be accepted.