In tip 050 and it's links, we were able to block access to specific drive letters.

By default, every process has access to floppy disks and CDs, so programs, services, and batch scripts can access them. You can restrict access to these devices to interactive logons only by using the AllocateFloppies and AllocateCDRoms registry entries at tip 237.

Note: You must restart the computer for this to take effect.