Connie, Troy, Michael, & Robert: thank you! I followed all your sugge
stions.

- SL is indeed on hda4, boots fine from grub installed in other OSs (I ha
ve 
2 such extra instances, on hda1 and hda5, both Debian stable), I just nee
d 
to set root, kernel and initrd to fit SL on hda4, and SL boots perfectly

- from the other systems and from within SL, once running, fdisk shows hd
a4 
where it should be, in the 2nd position on the HD

- grub (package) WAS installed during the fresh install, stages are visib
le 
in /boot/grub, stage1 is there, 512 bytes long

- once SL runs, by issuing

	grub-install /dev/hda4

grub attempts installing the bootloader to hda4, but complains that /boot
/
grub/stage1 is not read correctly

- this repeats even if
* grub package is uninstalled and reinstalled via yum
* as above, plus renaming of file /etc/grub.conf and of directory /boot/g
rub

- I also got to the grub prompt in the running SL system and used it 
interactively pointing to hda4 a.k.a. (hd0,3):

	root (hd0,3)
	setup (hd0,3)

the result is:

  Checking if "/boot/grub/stage1" exists... no
  Checking  if "/grub/stage1" exists... no
  Error 2: Bad file or directory type

- using the find command in grub WITHIN THE RUNNING SL SYSTEM should have
 
detected the other 2 instances of stage1

	find /boot/grub/stage1

but the result was consistently

  Error 15: File not found

- using the find command in grub in the bootloader of the other 2 OS's 

correctly detects all instances of stage1 on hda1, hda4, hda5

- I repeated the bootloader install from the grub prompt of the two other
 
OS's on the same spindle, it does find stages and installs the bootloader
 
onto the SL partition, however after rebooting the SL partition I only ge
t 
a grub boot prompt that wasn't there before, but it can find neither kern
el 
(for booting automatically or manually) nor stage1 (for reinstalling).

To sum it all up:
- hda4 is the thing, grub package is "installed"
- SL grub package can't finds stages nor install bootloader
- non-SL grub finds stages in all partitions and somehow installs grub on
to 
hda4
- once thus installed, the bootloader on hda4 produces the prompt, but 

still can find neither stages for installing, nor kernel etc for booting 

(even tried --recheck)
- non-SL bootloaders boot SL fine, a clear provocation on part of that 

other distro.

Using a non-SL bootloader is too dirty to contemplate! What should I look
 
at next? TIA, Filippo