[plug] How to install grub on an external disk, so it boots as primary.

[Mike Holland]

Hi folks,
I'm far from home with a CD-less laptop and a USB external drive full of 
data.
I have copied Linux and my essential data from laptop to the external
drive, and wish to make it bootable as a backup, in case the primary fails.

  However I cannot see how to install GRUB so that it
can be swapped to the primary drive. Ordinarily, I would boot off
CD with the new HDD installed, but this laptop has no optical drive,
and I'm out in the wilderness without another Linux PC to use.
  The laptop BIOS will not boot from USB-mass-storage.

So, Is there a way to get grub to install on sdb for booting as sda?
Or should I try LILO?

Mike