Unlike SP2, there's no installation tool for installing SP3 on an SBS 2008. Fortunately, the installation is pretty straight-forward. The steps to perform depend largely on whether or not your SBS 2008 server is running Forefront Security or not. If it's not, simply install SP3 like you normally would. The installation will succeed without additional tasks. If you are running Forefront Security, you will have to disable it before installing SP3, then re-enable it when installation has completed.

Things to do first

1. Download SP3: http://www.microsoft.com/download/details.aspx?id=24111.
2. Run the software, it will extract its contents to a directory of your choosing. I recommend creating an empty directory as the package won't do this for you.

Disable Forefront Security

If you don't have Forefront Security, skip this step.

1. Stop the following services:
   • FSCController
   • Microsoft Exchange Information Store
   • Microsoft Exchange Transport
2. Open an elevated command prompt, navigate to the folder C:\Program Files (x86)\Microsoft Forefront Security\Exchange Server.
3. Run the command: fscutility /disable. You should get some messages like so:

Removing dependencies...
dependency on FSCController removed from Microsoft Information Store
dependency on FSEIMC removed from Microsoft Exchange Transport Service
Microsoft Exchange Transport Service Agent registration removed

Status: Microsoft Forefront Server Security NOT Integrated.

Install SP3

Run setup.exe in the unpacked folder of SP3, and follow the installation wizard.

Enable Forefront Security

If you don't have Forefront Security, skip this step.

After installation of SP3, follow these steps to re-enable Forefront Security:

1. Stop the services:
   • Microsoft Exchange Information Store
   • Microsoft Exchange Transport
2. Open an elevated command prompt, navigate to the folder C:\Program Files (x86)\Microsoft Forefront Security\Exchange Server.
3. Run the command: fscutility /enable.
4. Start the Exchange services:
   • Microsoft Exchange Information Store
   • Microsoft Exchange Transport

Finishing

Don't forget to install the latest Update Rollup via Microsoft Download (select the latest from the list).

Additional info about installing SP3 can be found here: http://support.microsoft.com/kb/982423.