re-enabling root and disabling plain user

[MER]

Hi,

I want to make my Ubuntu box behave like a "classic" linux box when it
comes to admin tasks privileges.

I re-enabled the root account, but now, when I launch admin-related
tasks, sometimes the system asks
for the root password and some other times it asks for the user password
("enter your password", like default
Ubuntu).

How can I set things so only the root password is demanded when
accessing and admin task (and my default user denied
from doing it)?
Should I just remove the adm group from my main user, or will that wreck
havoc?

Thanks for your input.

Marc