Today we posted guidance on using an existing WSUS server from an Configuration Manager deployment for FCS definition distribution. The complete guidance, Deploying FCS definition updates with a shared System Center Configuration Manager WSUS infrastructure (http://technet.microsoft.com/en-us/library/dd185652.aspx
), can be read on TechNet.
Refer to Supported configurations for using WSUS to distribute Forefront Client Security Definition updates within System Center Configuration Manager 2007 (http://support.microsoft.com/default.aspx/kb/958491) for supported FCS and Configuration Manager shared configurations.
Also, we are announcing support for definition distribution via WSUS 3.0 installed on an x64-based platform. To support this configuration, the FCS distribution component must not be installed on the x64-based WSUS 3.0 server, as WSUS 3.0 does not require the installation of the FCS distribution component. Existing FCS documentation will be updated accordingly.