I have upgraded four B&ws in the past year and the one common problem I had with all four machines was that the ram that had served without problem for years in os8 and os9 caused nothing but problems in osx. Either with jaguar or panther. I'm not saying that this is your problem, but
that is the first place I would look. In all four machines I ended up chucking all of the ram sticks
and putting in ram from Crucial. I got the idea for Crucial ram from the old apple B&W tech forum.
Once the Crucial ram was in the crashes stopped and all four machines became solid as a rock in osx.
I did this process one machine at a time trying to spend as little money as possible and each machine I upgraded had crashes and freezes until I changed out the ram.
I guess the bottom line of what I'm saying is try different combinations of the ram you have and see if you can get it to work. Maybe try one stick at a time to see if that changes the situation. I was always able to get certain combinations of my old ram to work well most of the time but still had annoying crashes every so often until I came to the conclusion about the old ram. Good luck on figuring out the problem. I know from experience that the B&Ws can be very finicky when you are trying out different things, but once you get them dialed in they are very dependable.
Also, if the machine is a rev 1 and you put an ata drive in you would be wise to use a pci ata controller card, as the onboard controller is problematic. You can read all about this at xlr8yourmac.com. There is a ton of info on the B&Ws there.