Slow logon

I have just upgraded our NT domain to a Windows 2000 Domain. I am having a problem with some Win2k machines logging on extremely slow. All of the NT and 95/98 machines log in fine. I am running sp2 on the 2k machines and they all have 3c905 10/100 cards in them. I am running the Netbeui protocal also but it does not seem to help either way. Any ideas?????