My experience doesn't quite match other posters reporting
similar bugs.  In my existing Red Hat 6.0 system, I don't
have any NTFS or HPFS partitions, and the root is on the
first drive, but the installer still fails.  It says
(quoting from memory, sorry) "I can't do an upgrade because
you have no existing Linux partitions".  I don't find any
other error messages, and it does not retry looking for
existing partitions.

If I press Ctrl+Alt+F2, create a device node for /dev/hda,
and look at it with fdisk, fdisk sees all the partitions
correctly.

Here is my fstab:
/dev/hda5   /              ext2    defaults             1 1
/dev/hda1   /c             vfat    gid=30060,umask=002  0 0
/dev/hda7   /d             vfat    gid=30060,umask=002  0 0
/dev/hdb5   /e             vfat    gid=30060,umask=002  0 0
/dev/hda6   swap           swap    defaults             0 0
/dev/fd0    /mnt/floppy    auto    noauto,user          0 0
/dev/fd1    /mnt/fiveinch  auto    noauto,user          0 0
/dev/cdrom  /mnt/cdrom     iso9660 noauto,ro,user       0 0
/dev/cdrom2 /mnt/cdrom2    iso9660 noauto,ro,user       0 0
none        /proc          proc    defaults             0 0
none        /dev/pts       devpts  mode=0622            0 0



------- Additional Comments From   10/16/99 22:46 -------
The problem occurred because my /dev/hda5 is an extended partition
inside a primary partition of type 0xf, as discussed in the comments
on bug 5555.  I was able to do an upgrade by temporarily changing the
primary partition type.