[sudo-users] Password rejected, sudousers correct?

[Oliver Iberien]

Hi,

I've just installed Mandriva 2006, and edited the users file with visudo:

# User privilege specification
root    ALL=(ALL) ALL
oliver  ALL=(ALL) ALL
# Uncomment to allow people in group wheel to run all commands
 %adm   ALL=(ALL)       ALL

sudo keeps rejecting the root password anyway. In the troubleshooting FAQ, 
there is some stuff about "shadow passwords," which I think are standard for 
linux(?). It says to look in a conf.h file that I can't find.  The 
instructions that follow are beyond me. 

I can't imagine I am the only person with this problem, but Google and your 
archives turn up nothing. Any help would be much appreciated. Please cc: my 
address in your reply; I'm not on the list. 

Thanks!

Oliver