Note: Here I assume that the root.img and boot.img -files in
official RedHat ditribution (ie. CD-ROM) are identical with
those found in ftp.redhat.com. If that is not the case this
applies only to the files found in ftp site and its mirrors.

If there is already more than one DOS/Win partitions on the
disk(s), install program writes a section for all of them in
/etc/lilo.conf.
Problem is, that is gives all of them same label and lilo
refuses to understand that.
Result is that install program pops up an error in
"installing lilo" stage.
Install program continues othervice normally and quits
cleanly, but lilo will (of cource) not boot the system after
reset as expected.

Trivial solution is to use "custom boot" -disk and manually
clean up /etc/lilo.conf.
But I think it is not the first thing a newbie
wants/can do :)

It may well be that if DOS partitions are not marked as
"assessible" within install program, this bug won't appear.

I have heard at least two other people having same problem.
One of them had scsi disks and was upgrading from
RH5.1. Problem was still excactly the same.
(My system was normal pentium with two IDE disks)