We recently ran into an issue concernig an Automatic Security update for Windows 2003 and WSS 3.0.  The customer's SharePoint site became inoperative and displayed a 'Cannot connect to the configuration database' error.  The server Application Log showed a Windows SharePoint Services error of 'Unkown SQL Exception 33002' - 'Access to module dbo.proc_getObjectsByClass is blocked because the signature is not valid.'  Turns out that this was caused by a security update for Windows SharePoint 3.0 reference KB934525.  If this patch is applied you have to run psconfig -cmd upgrade -inplace b2b. This utility can found under Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\Bin .  Please reference KB934525.

Ron