Mapping to Network resources

Users are remoting into a Multi-master NT domain through a Nortel VPN switch using IPSEC tunneling – various methods of connecting, dial-up to broadband.
Some (mostly 98 and ME clients but some Win 2k) cannot map to network drives. They are loggingon to their respective domain remotely, can ping by name and IP, but not see server with a find or map – ‘no path to server’
Have set DNS, WINS, even host files in some cases. It will work once and on reboot fail again with path to server error.