Thanks for all your thoughts and suggestions.

I never really thought much about the formatting on the external USB drive, but it could certainly be the cause if it wasn't formatted as a HFS volume.

Fortunately I have a USB to SCSI converter which I could use to hook up an external SCSI drive (which is a known HFS volume) and copy them across from that. Another thought might be to simply compress the files into a stuffit SEA and copy them across like that - that should keep the resource fork intact.

I'll do some experimentation I think and report back on how I get on.

Cheers!