Thanks Jacky, sorry for the long delayed response, but these two services are set up as you advised.
I've also checked "Remote Porcedure Call RPC", it is started and set up to start automatically; however am unable to stop it as all options are unavailable, however this service is unavailable for change on all my other networked PCs where the Vista Security Center main window can be opened. ("DCOM Server Process Launcher" is started, as an FYI). Also, "Security Center" service (Automatice Delayed startup) and "Windows Management Instrumentation" (Automatic) services are both started, stopped and restarted both of these services and rebooted.
I also received a Microsoft Vista Registry key fix file for the wsc and imported that into my registry.
Still despite above I'm unable to open the main Vista Security Center window from "Start>Control Panel>Security>Security Center". I get as far as Security, but when I click on the main "Security Center" header, I simply get the quick circular waiting icon and nothing more; no error message and the main window does not open.
I am however able to open all of the subclasses under "Security Center" except for "Check this computer's security status"; I receive the same quick waiting icon bnut no response.
Dave