admin/sudo confusion

[rikona]

Just installed 12.04 on a newly built box. Mostly working fine. Has 2
users. The first/setup user is an admin, the second, user B, was set
up as not an admin. LOTS if files for B were copied from the old 10.04
box, and B will be the main user. But, in the meantime, it would be
nice if B could use sudo to help with the setup of the box. So, I
installed users and groups, and set B to be in the sudo group [it is
listed that way too] - doesn't work though. Then set B to be an
administrator [temporarily], and B is listed as an admin - sudo still
NG.

To add to the confusion, 'user accounts' lists B as 'standard' even
though 'users and groups' has B as an admin. What's going on?

How can I get B to have sudo and/or be a temporary admin?
  
Thanks,

 rikona