I finally dumped NAV 2004, even though I had 11 months left on my virus subscription service. It was slowing down my system, and got even worse after I installed SP2 for windows. I had it running without autoprotect, and without many other options. Even with its automatic update and scheduling features turned off, LU1COMS~.EXE (or something close) kept popping up.
In my opinion, NAV is probably exellent at virus detection and I've been using Norton/Symantec products since my 386 DOS days, but its overhead was getting too much for my tastes.