Low resources

I am an outside consultant to a firm that has a large (100+)work stations on a pier to pier network. They use a vpn tunnel to access a large data base and have dsl from a local provider. My question concerns the resources on these individual pcs.The resources are always low. These pcs are always on the net, always sending and receiving e-mail and always conected to the data base. Short of a complete shut down are there any suggestions as to maintain a higher level of availiable resources?