I don't have a lot of experience with Old World Macs and Linux, but last I checked NetBSD still "just worked" with the 7(3,5,6)00. The kernel will need a bit of modification to enable the backside cache on the G3 card, but it should boot without that. Note that NetBSD doesn't support the 601 card. You need to be a bit of an OpenFirmware jockey, though, and dual booting is tricky. Still, it has the best persistent support IMHO; I don't know how well the PPC Linux distros support Old World any more, if at all.