Macintosh bootable volumes are supported on the internal 2-port PCI card (part number TSATA) but are not supported on any of the other SATA cards at this time.
Tempo SATA X4P and Mac OS X 10.4 requires the final version, 10.4.11 for tested functionality. For example, a RAID 1 set does not function under Mac OS X 10.4.6 in a Power Mac G4 Quicksilver.
This does not happen often, but sometimes the driver caches do not get purged and the new SATA driver does not get loaded correctly from ROM.
Try this:
1) Delete and empty trash for the following file and two directories:
/System/Library/Extensions.mkext (a file)
/System/Library/Caches/com.apple.kernelcaches (a directory)
/System/Library/Caches/com.apple.romextensions (a directory)