MS has released a planning tool for OCS 2007 Edge server deployment.
The tool askes a lot of questions about certificates IP addresses and othe infrastructure related items, and generates a report based on your answers.
Its a nice tool to get an overview of tasks and configurations needed to deploy the Edge Server role
Get it here:
The Edge Planning Tool for Microsoft Office Communications Server 2007 provides settings for configuring your perimeter network based on information that you provide to the tool.