Well, there doesn't appear to be any way to turn off active protection (or at
least the anti-virus part of it) in Pest Patrol. So, I enabled it and, of
course, that didn't remove the problem. Next, I manually edited the registry,
removing any subkey where AV_DVP appeared. This finally made all the error
and warning messages disappear from the logs -- except the following one.
(Any ideas on how to get rid of it?)

Event Type: Warning
Event Source: Userenv
Event Category: None
Event ID: 1517
Date: 11/6/2005
Time: 2:04:52 PM
User: NT AUTHORITY\SYSTEM
Computer: MAIN
Description:
Windows saved user MAIN\[my username]registry while an application or
service was still using the registry during log off. The memory used by the
user's registry has not been freed. The registry will be unloaded when it is
no longer in use.

This is often caused by services running as a user account, try configuring
the services to run in either the LocalService or NetworkService account.