With the SCSI Nikon I tried hooking up via an Adaptec PCMCIA to SCSI adapter I learned that the Nikon specifically needs to be connected directly to a PCI SCSI card. USB to legacy adapters tend to be flakey anway.
On e-bay you'll notice that Nikon USB equipped scanners now command serious prices while SCSI ones don't -- blame Apple for abandoning SCSI.
If you can, I would add a PCI Adaptec card to your computer.
The Adaptec used to work okay,but my G5 crashed and in the process of restoration the hard drive was formatted, I am wondering if running OSX 10.4.11 now, the adaptor is still compatible. I think this is the latest OS that you can still utilise Classic 9. Sorry I am a little slow in these matters
I found out that the Adaptec only works with OS 8,9 contacted them to see if they have an alternative. I will try the PCI to SCSI card, failing that I have located an older G4 that has OS 9, so one way or another I will keep on trucking,thanks for your help.