Our SBS MVP Google-King, Merv Porter, has some good advice as to when to install service packs/security patches while installing SBS.
Service Packs are cumulative (see ‘Road Map’ link below). So, you can substitute Windows 2003 SP2 for SP1 during the install procedure for SBS
2003 SP1 (see below). You can also substitute Exchange 2003 SP2 for SP1 in that procedure. Generally, it is not recommended to allow servers to be
updated “automatically” from Windows Update. Also, when installing SBS from scratch, it’s recommended to install the base OS (CD1), then complete the
SBS component setup (Contrinue Setup icon on the desktop), then do the Service Pack installs and Windows updates.
Windows Service Pack Road Map
How to install Service Pack 1 for SBS 2003
After you’ve installed SBS 2003, download and run the SBS 2003 BPA to see if it can find any problems with your installation or configuration.
Microsoft Windows Small Business Server 2003 Best Practices Analyzer
How to Use the Windows SBS 2003 BPA
SBS BPA Known Issues/Common Questions