Microsoft-ds on port 445

I have a NT4 network with 1 domain and some win2000 box and some winxp box.
Sometimes it happens that I see many packet between my winxp oc and an win2000 or winnt pc/server; these packets have "Microsoft-DS" protocol, port 445 and other port.

I inserted MaxWorkItems=256 in registry, but nothing is changed.

Could someone explain me this fact?

Thanks!

Port 445 is used by Win2k for everything that used to be port 137 (NetBIOS name service), port 138 (NetBIOS datagram) or port 139 (NetBIOS session, print and file sharing).