Recently I have had to configure a virtual environment for IFD to test a MSCRM 2011 solution I have developed. The solution had to work on the internal domain as well as externally. Below I have listed the steps I went through to get IFD working internally and externally on the same machine. Please note that these steps worked for me and my scenario/setup. They may help as a guide for your deployment. This guide expects you to have some knowledge around DNS, Certificate Management, Internet Information Services and Microsoft Dynamics CRM.
In Microsoft Dynamics CRM 4, to make CRM externally facing you had to configure the internet facing deployment tool. This would enable you to access CRM externally through forms based authentication. In Microsoft Dynamics CRM 2011 Microsoft have decided to ditch forms based authentication for claims based authentication.