Having had a read around on www.linux1394.org, I've downloaded the rescan-scsi-bus.sh script. Runnig this causes /dev/sda to be attached to the 1394 HDD. Don't yet understand why this is needed, RH9 doesn't have the script and copes with the attachment of the SCSI device files. Roll on 2.6 (the hotplug SCSI stuff has been revamped apparently).