Microsoft made the RCO (release candidate 0) version of its upcoming Windows Essential Business Server (Windows EBS) 2008 available recently, and now SBS 2008 RC0 is available as well:

Brief Description

Public Preview Software – Release Candidate 0
Designed for small businesses, Windows Small Business Server 2008 is an affordable, integrated server solution that helps you protect your business data, increase productivity and present a more professional image to customers – giving you the tools you need to help grow your business capacity.

Overview

Windows Small Business Server 2008 (Windows SBS 2008) is an integrated server solution that helps you protect your business data, increase productivity and present a more professional image to customers. By providing many of the features used by larger companies --e-mail, an Internet connectivity, internal Web sites, remote access, support for mobile devices, file and printer sharing, backup, and restore--Windows SBS 2008 gives you the tools you need to help grow your business.

Windows SBS 2008 is available in two editions: Standard and Premium.

Standard Edition includes the software to install the primary Small Business Server.

Premium Edition includes software to install an additional Windows Server (either x86 or x64) for your domain, with the option of running SQL Server.

You can read more about SBS 2008 (and EBS 2008) in my SBS/EBS 2008 preview series.