Windows 2000 Security on LAN

We have got a LAN using a Windows 2000-based server. We’re going to manage users’ accesses. We can do that by determining each user security level, letting or denying users’ grants. But we couldn’t find a way to manage special computers in our LAN. In other words, we can not determine that some especial users could have more privileges than others. For example, we have a group which its members have no limitations to work with 3 machines (not others). How we can change our security level to client machines, so each user may have some especial accesses to some determined computers?

Thanks