What you are looking for is something called a Fan Gate.
A Facebook fan gate is also known as and often referred to as the reveal tab or welcome tab. Sound familiar? In fan pages for Facebook, the fan gate is the initial tab (or landing page) new visitors to your page land on. It’s not for returning fans, strictly for new visitors. Once they “Like” your fan page for facebook, and become an official fan the fan gate tab turns into different content that is available to fans only.
You use to be able to make them yourself with some FBML and the FBML app on your page, but that app is no longer available and has been replaced with the iFrame app.. thus requiring a bit more coding to get it to work.. or going a pay solution.
Here is a link to a step by step php iFrame free solution
Here is a link to a step by step solution provided by Wildfire http://www.marismith.com/iframes-facebook-app-fan-gate-wildfire/