by Thanks to all who responded to the above problem. Here's the shortest
solution, synthesised from the responses, that worked for me.
When installing Linux, if you have no scsi devices other than the zip drive,
choose no scsi devices when asked.
insert into the /etc/rc.d/rc.local file the lines:
/sbin/insmod parport
/sbin/insmod ppa
create the directory /mnt/zip
insert into /etc/fstab the line:
/dev/sda4 /mnt/zip msdos noauto 0 0
then, reboot.
If you then type:
mount /mnt/zip
this should give you a working zip drive on the directory /mnt/zip
(hopefully)