Hi

Thanks dean-dean for your response.

I've followed your instructions and have finally come to a point where I
receive a "WMI repository is consistent", having gone through the
"salvagerepository" step. This has helped in ensuring that the Security
Center recognizes Windows Defender as functioning. However, it has not aided
in recognizing Norton 360. As such, I am compelled to resort to security
freeware, as recommended by PCworld.com, such as Avast Anti-virus, ZoneAlarm
Firewall in addition to SpywareBlaster as well as Spybot - S&D. I still have
my Norton 360 product key should I wish to reinstall it though.

It very well seems that brink is right in saying that "Norton has been known
to cause problems with Vista." At present, the Security Center is running as
it should, reporting that I now have Firewall as well as Malware Protection.

Thanks to all who've helped so far