installation failing if using CD-R

[egf at RiskProof.hn.org]

I am unsuccessful installing FreeBSD 5.3 on an Intel x86
box which has only SCSI peripherals.

If I insert Installation CD #1 into the CD-Writer drive, 
it boots up successfully into the install program. The drive 
is a PLEXTOR CD-R  PX-R412C.  It proceeds OK down to the 
screen titled "Choose Installation Media". If I select item:

    1. CD/DVD  Install from a FreeBSD CD/DVD

and then press <CR> it just repeats the dialog, and refuses 
to find the installation images on the very same CD that 
it just booted from in the first place?!   And, there is 
no other device choice given which is applicable here.

I even went so far as to retry an install from FreeBSD 5.2.1
CDs which I had previously installed onto an ATA-based box.  
It failed in exactly the same place with the same error.
What gives here?

This system has all SCSI peripherals: the controller is a
Tekram PCI board model DC-390F with Symbios 53C875 chip,
3 HDDs and the Plextor CD-R.  

This same box was previously been running RedHat Fedora Core 1 
for over a year with the same h/w config.  Now, I wish to convert 
this into a FreeBSD firewall system running PF.

thanks,

ed