Remote access to Windows NT 4.0 servers?

I have a number of remote dial-in users, Windows 98 and Windows 2000 notebooks, who connect to the Windows NT4.0 server via dial-in ISDN circuits. The system consists of a Cisco Router with Cisco PIX thru an Intel Switch and hubs. The problem is this: The Router answers and passes the connection to the Server where User Name and Password are authenticated. Now the problem…. Upon completion of the authentication the network is not displayed in the network neighborhood and you can’t map drives. The system worked correctly before the Windows NT4.0 servers were replaced with new CPUs therefore I believe something was left out when the new servers were configured. I have checked User Names, Passwords, etc. but can’t identify the problem. Any suggestions would be greatly appreciated.