Bonk, I think I know what you mean, about the on demand AVs and software firewalls.  I currently use Norton AV and Personal Firewall; I hate their invasiveness but like Will Weasel said, it's better than getting blasted three times every two days.  I am using a firewall router, too though, so maybe the soft-wall may not be too necessary.
What would you recommend, however?
It looks like you and I are at the same place with Norton.  I'm getting ready to install WinXP this week so my spouse can play with Photoshop/Premiere, so I need to figure this issue out soon.  The problem I have is that sometimes I take my system over to a friends house to play games.  This sort of forces me to purchase a software firewall and a antivirus as I don't always know the people that are there on any given day or the setup they have.  I have a hardware firewall built into my router (Netgear FVS318), it is not perfect but it seems to do pretty well.
The thing is the more I research this issue the more confused I become.  Kaspersky and McAfee seem to be tops as far as catch rate goes according to the graphs in the 
link I posted another thread.  But Kaspersky I told can be a pain to configure and you can only buy it on the web.  McAfee is a resource hog and was totally unstable on my Win2000 setup plus there help desk was reading from a script.  Now when I read the reviews from CPU and Maximum PC, I found PC-Chillin kept popping up as the best for 2005.  
Virus Bulletin has also given PC-Chillin good marks lately as well.  However the trial version of PC-Chillin I received with my motherboard (18 months ago) was totally unstable.  Virus Bulletin also gave PC-Chillin a failure rating around the same time period for WinXP.  So I have to wonder if PC-Chillin is on solid ground now or are they just hitting a momentary peak.
If you haven't guessed yet I am researching all of this as I am writing this post.  *sigh*   

Well I'm wiping the hard drive today so I'll let you know what I come up with tonight.  I'm putting WinXP on another hard drive so my current Win2000 setup will be unaffected.