Breaking out of menu on "live disk", repairing grub

[Simon Hobson]

This is probably something really simple I've missed, but ...

Sometimes I have to try and repair systems, and often it is "just" a matter of 
booting it with another grub and then running grub-install on the system so it 
can repair it's own grub. But, for something like a Debian Live disk, I can't 
see how to break out of the grub menu and get to specify my own kernel and 
initrd lines.
The specific case is where I've copied all the files to a new machine or disk, 
so everything is there but the bootloader. Or the bootloader is damaged in some 
way.

Also, back in Grub 1 days, I could remember how to install grub just by 
mounting the filesystem, chrooting to it, and issuing a few grub commands. I've 
never managed to make this work with 1.99 (as currently installed with Debian). 
Is there a simple set of commands that will do what worked in grub 1 (going 
form memory here) :
hd0 = /dev/sda
root = (hd0,0)
install (hd0)