System Policy Problems

To increase the security on our network I have implemented a System Policy on NTServer and workstations. I have hidden all drives apart from the network user drive. However some of our user’s need to be able to save to a directory on their C:drive. Ideally I would like to find a way to map a drive to just that dir through the logon script. I have tried to do this through Control Panel/System and creating an environemnt variable but have had no success. I know a simple solution would be to allowthem to see the whole c:drive but I would like to avoid this for obvious reasons. Any ideas would be willingly received.