Mapped Drive Not Responding

Hi,
I have win2k srvr and win98,win2k clients. Some of the
shared folder is mapped to win98 clients. Win98 clients
are taking advantages of this shared folder as mapped
network drive. The problem is if they are not using their
computer for more than 3 hours(approx), then this mapped
network folder is no more responding. They have to restart
the PC to get back the things. Only TCP/IP protocol is
installed on client machines. I disable the power saving
mode of the network card still same problem.
pls anybody can hlp

Thanks in advance

APK