Ok this time you need to be ready for migrating your facebook apps to IFrame based apps, as it written on Facebook Developer Roadmap that facebook,
“We will stop allowing new FBML applications, but will continue to support existing FBML tabs and applications. Instead, we recommend using IFrames.” at the End of 2010.
And then OAUTH 2.0 will required for new applications,
“We will remove the ability for new applications to use our old authentication mechanism, but will continue to support existing applications using our old method.” at the End of 2010
Take a look at Facebook new PHP-SDK on github, that might help your life easier.
Here we go then, I suppose you already know how to “set up a new application” , just go to http://www.facebook.com/developer ,
Important things you should not miss:
Go to “Website” Tab, fill in the Site Url with your callback url.
Go to “Facebook Integration” and then pick Iframe for canvas type
Use the new PHP-SDK,
Or maybe you want to make a bootstrap function for an easier call,
Thats it , hope it help.