After installing Sharepoint 3.0 SP2 (KB 953338), when you browse http://companyweb or open Sharepoint 3.0 Central Administration, you receive the following error "Cannot connect to the configuration database". After you install one of the following updates or service packs on a computer that is running Windows SharePoint Services 3.0, you may have to rerun the SharePoint Products and Technologies Configuration Wizard (Psconfig.exe):  Windows SharePoint Services 3.0 software update, Windows SharePoint Services 3.0 service pack

More info: SBS blog