those are two different questions.
a quote from the Leopard security configuration guide (to disable USB drives at all):
48 Chapter 3 Protecting the System Through Hardware
Removing USB Support Software
Use the following instructions to remove USB mass storage device input/output
support such as USB Flash drives and external USB hard drives.
The removal of this kernel extension only affects USB mass storage devices. It does not
affect other USB devices such as a USB printer, mouse, or keyboard. This task requires
you to have administrator privileges.
Important: Repeat these instructions every time a system update is installed.
To remove kernel extensions for specific hardware:
1 Open the /System/Library/Extensions folder.
2 To remove support for USB mass storage devices, drag the following file to the Trash:
IOUSBMassStorageClass.kext
3 Open Terminal and enter the following command:
$ sudo touch /System/Library/Extensions
The touch command changes the modified date of the /System/Library/Extensions
folder. When the folder has a new modified date, the Extension cache files
(located in /System/Library/) are deleted and rebuilt by Mac OS X.
4 Choose Finder > Secure Empty Trash to delete the file.
5 Restart the system.
to require and admin password on a nonadmin account. use this link to get Server admin tools
http://www.apple.com/downloads/macosx/apple/application_updates/serveradmintools 1057.html
Then open Workgroup Manager. Enter
localhost in the address field, and an admin username and password in the remaining fields.
select an account whose access to USB you want to restrict, click on Preferences->media access and set it as you want.
