Network Disconnects

On the network at work we are having a problem with computers that are not active on the network all the time are getting disconnected. There are about 13 computers in all and only about four of these dont have this problem, but those are the computers that are active on the network almost all the time. This is a fairly new network, the server is a win2000 and the rest run win 98, 98 SE and 95. I dont know the details aboutthe network, the only thing in common with the ones with problems are they are not always active on the network. I am not much with networks and neither does it seem that our network guys are either. Any kind of ideas or if more info is needed, I would appreciate ANYTHING
Thanks