A good bet is probably search the MSDN

Welcome to the Windows SharePoint Services 3.0 SDK
http://msdn2.microsoft.com/en-us/library/ms441339.aspx

Programming in Windows SharePoint Services
http://msdn2.microsoft.com/en-us/library/ms430674.aspx

Data Storage in Windows SharePoint Services
http://msdn2.microsoft.com/en-us/library/bb897648.aspx

The Windows SharePoint Services Object Model is mentioned there, which is a good sign.

An interesting quote:

Windows SharePoint deployments use Microsoft SQL Server to support a site collection's content database. However, under some circumstances, it can be more efficient and cost-effective to store some of the site data in an external data store.