Shared internet access

Using Sygate 4.0 and windows 98, I wish to give all local users (A, B, C, D) access to the internet and to prohibit one of those users (D) access to any of the hard drives on the system (A, B, C). At the same time I wish to allow other users (A,B,C)full access to the hard drives on A,B,and C. Any suggestions on how to accomplish this?