Win. 98 problem logging into Win 2K PDC

Hi! Here is my problem. I currently have about 40 workstations (WS) connected to an NT4.0 domain. OS’s range between 98 and WIN 2K Pro. Over the weekend we shut down the NT 4.0 domain and replaced it with Win2K domain. The PDC is running Active Directory as well as DNS and DHCP. During setup we configured all WS’s to point to the PDC IP for DNS. However all the 98 WS’s would not connect to the new Domain. Upon log in I would get an error saying “password is invalid or sever is not available.” And about 10% of the WIN 2K WS’s would say the same error. As a result we decided to switch back to NT 4.0 but now the 98 WS’s are not able to log into this Domain. The same error appears. Has anyone ever experienced this problem? This is weird!