Allow users to user their own usb key

Hi we are running windows xp sp2 with windows 2003 sp1

I want to allow certain users to use their own usb key even if they are

non-admin

I tried the GPO "Load and unload device drivers" and ive put the group

"Domain Users" on it. I tested that on a pc but it ask me the username and

password of an admin users

Any help please

Thanks

JAc