re: worm kills taskman, regedit and msconfig
This is something, I've come across, but haven't tried yet. I was planning to run it next time I came up against a nasty spyware. http://www.sysinternals.com/ntw2k/freeware/procexp.shtml
Take a look its supposed to give you lots of information about the processes that are running.
And from the same site is a registry monitor. Haven't tried it yet either, but maybe it will help you track stuff down.
http://www.sysinternals.com/ntw2k/source/regmon.shtml
I seem to recall the msblaster worm locking out the CTRL ALT DELTE and Regedit commands. Perhaps this is a variant?
Have you tried turning on Heuristic controls in NAV?
-Steve G.