Network changes

Recently our network was upgraded to 2000. Since then we have had problems with networked printers being very slow to respond, network drives open more slowly & computers crash more often. Our network administrator says it is the computers, not the network. (These are HP computers, Windows 95 or 98.) I am not a network person, I do very basic troubleshooting before bringing in other help. Is there something (basic trouble shooting) I could be doing to help my users & clean up their connections?