This may be old news, but I only came across it by accident so I thought I'd post a note here.
I read a review of a 10K RPM drive SCSI RAID setup on xlr8yourmac.com in which the reviewer mentioned he was using a Dell branded Adaptec 39160 dual channel Ultra3 SCSI card. He didn't say much about it other than he flashed it with Adaptec's current Mac firmware.
I picked up a PC 39160 off Ebay for under $50. I installed it in my Quicksilver, booted into 9.2 then downloaded and ran Adaptec's v1.2 firmware updater. Success! The card is now recognized in 9 and with a driver download, in X.3 as well.
320MB/s (2x 160MB/sec channels) for under $50.
Now I need to decide whether I want 10K RPM drives in the G4 or if I should go external because of heat concerns.