Hi there,

>this time however, i can't su to root.
>
>  $ su - root
>  Password:
>  Sorry
>
>i *know* i'm using the right password, since i can login as root on 
the console
>without any problem.

I know it's obvious, but one tends to ignore the obvious far too often 
;-)
Is the account you use in group 0 ?

have fun
Michael