I guess I should have been clearer. I am fully aware of the world that Limewire opens to my kids - our computer is in a location that can be easily monitored (not a bedroom). I trust the kids, but I was experimenting with some of the new Vista features out of curiosity and came across the incompatibility with Limewire and parental controls. One thing the parental controls do provide is a nice quick way to see if any of the kids have run .exe's that I don't recognize. It also helps me see how long they are on the computer for.
I still have the Vista firewall enabled and also the hardware firewall that comes with my router - both work fine with Limewire. I do plan to look at some of the other anti-virus packages out there - I'll eventually get there (recommendations welcome, though it is out of scope for this thread).
The main reason for the post was to find out if anyone was familiar with Limewire's incompatibility with the parental controls - I'm sure my kids won't be the only ones who want to run Limewire and whose parents enable this feature.
I suppose it could be argued that the "incompatibility" is by design, since as you say Limewire opens the world of adult content to the kids. In the long run, it would be nice if Limewire somehow tied into Parental Controls - but that may be too complex to achieve. A nice start might be to not allow photo or movie downloads.