reinstalling mbr on root disk attached to a different machine

[Radu]

I'm trying to restore the GRUB MBR on a disk that I have rebuild and on which i
have restored the 3 partitions (root, boot, swap).  The problem is that the
disk in question is not "sda" as it would normally be during the boot process.
It is "sdb" because I plugged the disk in a recover machine via a IDE-to-USB
dongle.  (I have to do this because the original machine does not have CDROM or
floppy and attaching on is physically difficult.)

The question now is how do I get grub to install on sdb (currently hd1) as 
though
it was sda (hd0).  I have encountered a miriad of error messages as I tried
different scenarios.

My final solution, which I'm trying to avoid, is to remove the internal disk
so that the USB attached disk comes up as "sda", at that point everything works
fine.  The question is what to do when the first disk is not the target disk.

Is there some documentation on this type of grub install or does somebody have
experience doing this?

Details:
  Rescue CD:     systemrescuecd-x86-0.4.0
  Restored OS:   Centos5
  GRUB version:  0.97

Thanks in advance.