mapped network drives are disconnected.

On serveral of our machines (Win98 and 2000)we have just recently started to have problems with mapped network drives disconnecting at undetermined intervals. Once disconnected the user can still access the network and needed resources through network nieghborhood – but not
though the mapped network drives. Only when the user reruns the login script or logs off and logs back on do the mapped network drives reconnect. I have upgraded the 3Com NIC drivers; set autodisconnect to the max interval; turned off power-management on the NIC; and increased the poll rate of the NIC from 8 to 64 – all to no avail. Please, Please Help. I need as many suggestions as possible.

Thank You