Put the username into the the plugdev group either editing the /etc/goup file or
Code:
useradd -G plugdev username
It is possible to activate this by running some startup script like udev, hal, but I think you'd better go rebooting the system.
Ciao
edit:
Code:
useradd -g plugdev username
the previous add a user to a non existing group (and create it of course)