ESX Server 3 Installation Guide : Installing VMware Infrastructure Management : Preparing the VirtualCenter Server Database : Configuring Microsoft SQL Server 2005 Express

Configuring Microsoft SQL Server 2005 Express
The Microsoft SQL Server 2005 Express database package is installed and configured when you select Microsoft SQL Server 2005 Express as your database during VirtualCenter installation or upgrade. This is shown in Installing VMware Infrastructure Management Software. No additional configuration is required.
If Microsoft SQL Server 2005 Express is already installed, review the required database patches specified in Table 2-1. If you do not prepare your database correctly, the VirtualCenter installer might display error and warning messages.
See www.microsoft.com/sql/editions/express/default.mspx.
 
Note VMware recommends Microsoft SQL Server 2005 Express for small deployments only (up to 5 hosts and 50 virtual machines).