Win 2000 and losing network connection

Hello… I some older AMD K62 300 MHZ to 500 MHZ machines, and I have installed Windows 2000. The network connection will drop out, and I will lose access to the domain after X amount of packets sent/recieved. If I reboot the connect of course is established until the next drop out. This problems only seems to reside on a couple of machines. Any one have an idea what can cause this problem?