Removing password-based auth for login

[Stephen Tait <tait@digitallaw.co.uk>]

This is somewhat tangential to my other thread, which is by-and-large 
sorted now, but I thought it might be worth a repost since it is an 
entirely different problem.

I have a bunch of users that have now been set up to use SSH keys for all 
login purposes; however, they currently have password based auth as well, 
and I'm unsure how to turn it off just for these users, and googling for it 
has so far netted me a whole load of gumpf with little or no relation to this.

Is it just a simple matter of deleting the appropriate entries (i.e. 
changing sync:$1$6dsbjkfdbfjkdbfdjkdbkjgobbeldekgook:34692:0:999999:7::: to 
sync:*: etc etc...) in /etc/shadow and /etc/shadow-?It would seem likely, 
but I'm loathe to do it in case I b0rk the whole system up. And do I need 
to modify shadow and shadow-? I m unsure of how these two files relate to 
one another.

Again, cheers for any info

Tait, the perpetual n00b ;)