Username/Password Problems

I am having trouble at the company I work at with Windows NT Server 4.0 and 95/98 clients. On each Win95/98 client, we designated a password for the “C” drives. One read-only password and one “Full” password. Using the passwords, I can access anyC:\ drive from any other client, but when I try to access a client’s C:\ drive from the server, I get a box that asks me for the username and password. I have tried every possible combination, but I can’t access the drive. I am guessing that this is an NT security issue, but I can’t seem to get any answers.