>>The whole issue seems to be an IRQ conflict or something in that vein<<
And the IRQ of your SCSI controller is? I guess I'll assume the Hitachi is a SCSI drive as well. And I wouldn't rule out anything until I've tried another equal piece of hardware (or one you know works). PS do go bad from time to time even though rarer than most things.
***check the jumpers 1st then check em again***