As I'm sure most of you are already aware, System Center Configuration Manager (SCCM) 2007 is a 32-bit application.
Installing SCCM SP1 on 64-bit Windows 2003 and 64-bit Windows Server 2008, is of course fully supported. However, given that SCCM is still a 32-bit application, performance will not be as great on 64-bit hardware as a native 64-bit application would be. Therefore the recommendation to ensure best results, is to install 32-bit versions of Windows Server even when working with 64-bit capable hardware.
The sole exception to the 32-bit OS rule is the SCCM site database server. As there are no SCCM components required and as SQL 2005 SP2 is available as a 64-bit application it makes sense to install this on a 64-bit OS for enhanced performance.
Traditionally, with SMS 2003, best practice was to utilise a local copy of SQL to host the SMS database on the primary site server. When SMS 2003 was released disk performance well exceeded that of the network. Today this is no longer the case. Additionally SCCM now makes considerable more use of the CPU. Based on these to facts using remote SQL for SCCM is now a viable option.
I took this approach recently on a large SCCM implementation with the following benefits -