Microsoft Forefront Team has also announced a Beta release today - Microsoft Forefront Security for Exchange Server with Service Pack 1 Beta 2! You can read the details on their blog.
Here is a part of their announcement:
As a part of our ongoing deep integration with Exchange Server 2007, we are also unveiling Forefront Security for Exchange Server SP1 Beta 2. This Service Pack integrates multiple scan engines from industry-leading security firms into a comprehensive, layered solution, helping protect your Microsoft Exchange Server messaging environments from viruses, worms, spam, and inappropriate content.
Read more here.