Task Scheduler Engine hogging cpu/locking laptop

My husband has a Dell XPS that was pre-loaded with Vista Home Premium. He
has had no problems to speak of with Vista to this point, but is on a
business trip and has run into a big problem that we're not sure how to
troubleshoot and fix. Once he got to the hotel and got things set up, his
computer suddenly started maxing out at 100% cpu and then locks up
completely, won't let him into task manager to restart, goes to black screen
and he has to turn it off from the button. When running process explorer he
noted that the taskeng.exe was what was hogging the memory, but when he tries
to stop the service or disable to service all of the options are grayed out
in services.msc. If allowed to run and try to complete what it's doing, it
runs for up to and over 2 hours hogging cpu the entire time. He was getting
an error message that said "logon process has failed to create the security
option dialog"--failure security options with the black screen, only when the
task engine continues to hog cpu and he tries to restart through task manager
to stop it. That's when he gets the error and then the system locks up and
he has to restart from the button.
From the info we can find about this people are saying it's a conflict with
third-party anti-virus/firewall software not being Vista compatible. But, we
have CA Internet Security Suite 2007 which is Vista ready and we have had no
problems with the security suite up to this point (it's been on the system
for about 3 months.)
Anyone have any ideas as to what is all of a sudden causing this conflict,
and if its something we can accurately troubleshoot to keep from happening?
Also, how do we disable the task scheduler engine since it won't disable in
the services section?
Any help or suggestions appreciated, sorry if this is in the wrong forum area.