QUOTE
grub-install 'hdo'
is not correct
grub-install '(hd0)'
is.
that's a zero, and you forgot ()
BUT!!! you have a /boot partition don't you? See below
grub-install --root-directory=/boot /dev/hda
info grub>Installation>using grub-install
CODE
Installing GRUB using grub-install
==================================
*Caution:* This procedure is definitely deprecated, because there
are several posibilities that your computer can be unbootable. For
example, most operating systems don't tell GRUB how to map BIOS drives
to OS devices correctly, GRUB merely "guesses" the mapping. This will
succeed in most cases, but not always. So GRUB provides you with a
user-defined map file called "device map", which you must fix, if it is
wrong. *Note Device map::, for more details.
Unfortunately, if you do want to install GRUB under a UNIX-like OS
(such as GNU), invoke the program `grub-install' (*note Invoking
grub-install::) as the superuser ("root").
The usage is basically very easy. You only need to specify one
argument to the program, namely, where to install GRUB. The argument
can be either of a device file or a GRUB's drive/partition. So, this
will install GRUB into the MBR of the first IDE disk under Linux:
# grub-install /dev/hda
Likewise, under GNU/Hurd, this has the same effect:
# grub-install /dev/hd0
If it is the first BIOS drive, this is the same as well:
# grub-install '(hd0)'
But all the above examples assume that you use GRUB images under the
root directory. If you want GRUB to use images under a directory other
than the root directory, you need to specify the option
`--root-directory'. The typical usage is that you create a GRUB boot
floppy with a filesystem. Here is an example:
# mke2fs /dev/fd0
# mount -t ext2 /dev/fd0 /mnt
# grub-install --root-directory=/mnt '(fd0)'
# umount /mnt
Another example is in case that you have a separate boot partition
which is mounted at `/boot'. Since GRUB is a boot loader, it doesn't
know anything about mountpoints at all. Thus, you need to run
`grub-install' like this:
# grub-install --root-directory=/boot /dev/hda
By the way, as noted above, it is quite difficult to guess BIOS
drives correctly under a UNIX-like OS. Thus, `grub-install' will prompt
you to check if it could really guess the correct mappings, after the
installation. The format is defined in *Note Device map::. Please be
careful enough. If the output is wrong, it is unlikely that your
computer can boot with no problem.
Note that `grub-install' is actually just a shell script and the
real task is done by the grub shell `grub' (*note Invoking the grub
shell::). Therefore, you may run `grub' directly to install GRUB,
without using `grub-install'. Don't do that, however, unless you are
very familiar with the internals of GRUB. Installing a boot loader on a
running OS may be extremely dangerous.
QUOTE
I was too afraid to do the "lilo -u" command because I feared that if I uninstalled lilo and then got some kind of error messages when trying to install grub, I would then not be able to boot at all into Mandrake9.2 again. Thus I'd have to do a re-install again and lose all the work I've done for acpi and other things.

you know better than that! That's what cd1>rescue>Install the bootloader is for

which I'm pretty sure you've done b4, BTW. When you do
lilo -v
you are half installing lilo. Same as mentioned above. When you do grub-install, you are only sorta installing. Doing grub is REALLY installing to the mbr. From cd1 rescue mode, you are REALLY installing lilo

and for those that are curious, here's how to put grub on a floppy (also from info grub>Installation)
CODE
Creating a GRUB boot floppy
===========================
To create a GRUB boot floppy, you need to take the files `stage1'
and `stage2' from the image directory, and write them to the first and
the second block of the floppy disk, respectively.
*Caution:* This procedure will destroy any data currently stored on
the floppy.
On a UNIX-like operating system, that is done with the following
commands:
# cd /usr/share/grub/i386-pc
# dd if=stage1 of=/dev/fd0 bs=512 count=1
1+0 records in
1+0 records out
# dd if=stage2 of=/dev/fd0 bs=512 seek=1
153+1 records in
153+1 records out
#
The device file name may be different. Consult the manual for your
OS.