Users kicked off network

2 of our PC’s are constantly dropping their network connection and facilitating a reboot to log back in. NIC is set at same speed as switch/server 10/100 1/2 duplex, and we have reinstalled nic drivers. Does anyone know of a utility/software app, monitor program, etc. I can use that will show me what process, or activities occur right before that dropped connection occurs. The PC’s are Win9x, and the Server is Win NT 4x. Thanks in advance.