Effect of malice process's on AV & Firewall & RFS remote file sharing?

I've heard that some virus's, etc. can prevent your firewall or antivirus programs from working (in order to detect them). If this occurs, does the programs still act like they are working and really aren't? Like say they are scanning files or blocking ports when they aren't?

I'm using W98SE and have a problem with port 1025 listening (phone unplugged and not connected to the net). If I close ZoneAlarm Pro the port is not longer listening. They told me I have a trojan or something causing this, yet I haven't been able to get NAV or Pest Patrol to find one or see any registry keys or files for ones that relate to this port. That leaves RFS remote file sharing. Does that even work on a Windows computer and if it does is there any registry key that might give it away if one had been planted on me?

 

in the past, viruses that have attempted to disable AV's usually did so by corrupting associated files thus rendering the AV inoperable. The user would experience DLL errors or the program just would not start at all.

 

Thanks for the feedback, it takes a load off of my mind thinking the AV might act like it was working when it wasn't. I feel more confident of whatever is leaving this port listening isn't a trojan then.
This location: http://www.geocities.com/merijn_bellekom/new/netstatan.html shows where the firewall Tiny Personal leaves a port listening for connections from the TPF admin program (which is similar to what I have going on with port 1025) so hopefully their rep was wrong in saying their program didn't leave this port listening.
I will still be uneasy until I know for sure what is causing it.