i changed again the rules and permission files.
the last one does only change the device permissions and does not affect the partitions on it.
--> user was able to fdisk the device but not to format it after it.

now i changed it a little bit:
usb-storage storage devices are now primary done in usb-storage/ and only symlinked to /dev.
--> permissions can be set in permissions file :)
also the ide-floppies are now done in floppies/ and only symlinked to /dev tree
--> permissions can be set in permissions file :)

now it would be nice if someone could check if the new rules doesn't affect scsi systems in a bad way, that partions are mapped to group storage.
(i changed the bus detection from scsi to usb so it should not be a problem.)