During install, having a Zip drive apparently confused the installer. 
During partitioning, no mention was made of the Zip drive.  After package
selection and X configuration, I got:

Formatting / filesystem
Formatting /boot filesystem
Transferring install image to hard drive
Setting up RP transaction

Then I got a dialog box that said

Error opening /tmp/sdb: No medium found
 [ Retry ] [ Cancel ]

I clicked cancel, and after a minute or so it went on (the first time I had
this happen I rebooted before it went on).

The text console (Alt-F1) said:

Error
Error opening /tmp/sdb: No medium found
80


This system is all SCSI, with

ID 1: IBM DGVS09U (9G drive)
ID 2: Pioneer DVD-303S (DVD-ROM drive)
ID 4: Plextor PX-W124TS (external CD-RW)
ID 5: Iomega Zip 100 (external Zip drive)

This happened the two times I've tried installing on this system, so it
appears to be 100% reproducible here.  Let me know if I can test anything
for you.