I've been looking for an answer to this question for a while. I have an ACARD 6280M ATA PCI card in my G4. When I installed Panther I didn't install any drivers for the card, which I did when I first installed the card in Jaguar (formatted and installed Panther). It just worked fine after Panther was installed, sans drivers. I noticed that ACARD had updated their drivers since the last time I looked. The package says it was in May 2003.
My question is, are the drivers necessary? Even though all drives mount fine, I'm wondering if I need the drivers to get the most out of the speed of the card.
(...oh, and I'm running 10.3.2)