MBR and grub-install

[Bruno Costacurta]

Hello,

I'm trying to install MBR and GRUB on another disk by making (from a third 
disk boot):

grub-install /dev/sda
grub ---> root(hd0,0)
grub ---> setup(hd0,0)

commands are accepted but doesn't work as PC continues to boot on my third 
disk. As far I understand grub-install should install MBR and grub commands 
should configured it.

- problem history: I had a two-disk (with LVM & RAID) with Fedora-6. As I 
installed distribution CentOS on a new third disk I now boot on CentOS via 
MBR on this third disk.

- what I'm looking for : I intend to recover previous MBR+GRUB on /dev/sda ( 
from previous Fedora install + setup) and then install CentOS entry into this 
grub configuration.

Thanks for attention.

Bye,
Bruno