I tried removing my /boot partition from /etc/fstab altogether,
placing boot files in the boot directory under / (where the partition
had once been mounted).  This didn't change anything; I still get the
error.  I have a *lot* of other partitions; I don't want to have to
somehow remove all of them to get this upgrade to work (if it came to
that, I'd take the opportunity to repartition anyhow, and do a
complete reinstall).

It is not possible to perform a hard drive installation/upgrade to the
same partition that the source files are located in, otherwise you
will receive the error that is described in this posting.

If by "source files" you mean the RPMs, I'm upgrading from a Linux
Central CD-ROM with a boot floppy.  I'm not doing a hard drive
install.

I looked back at the original comment, and yes, it appears that that
problem was from a hard drive install (and therefore yet another
duplicate of bug 2504, reported several times here).  This one isn't,
however.

I tried it again, and when I got to the point where it complained, I
went over to bash, and I simply ran "umount /mnt" (where /dev/hda6 had
been mounted), and it worked fine after that.

*** This bug has been marked as a duplicate of 2504 ***