Since Exchange 2007 was made available there have been numerous questions in various forums/groups on the Anti-Spam and Antivirus capabilities. Well, Hub Transport and Edge Transport Roles come in with a layered approach and tight integration with Forefront Security.
Microsoft has a few demos to take you through the same:
Exchange Hosted Filtering Service and Exchange Server 2007 110 KB | 300 KB Antivirus Protection with Forefront Security for Exchange Server 2007 110 KB | 300 KB Managing Anti-Spam in Exchange Server 2007 110 KB | 300 KB
There are many more demos available on the site for Business Continuity & Compliance when it comes to the Built-in Protection.