NETBIOS & Traffic Problem

Have this essenario: We’ve W2K domain and all the workstations with W2K Professional, our ISP told us that we have an excesive traffic of NETBIOS, so that we have some crashes, our lan is so big, but all workstations haven?t installed the NetBIOS protocol only DHCP & DNS Server heve it in order to provede a directory service of all the PC’s conected to the lan. QUESTION:What can I do in order to reduce te NetBIOS traffic and also the net crashes without affect the PC’s directory service????….. 😀
Thanks!!!! so much!!!!!!!