I'm just migrate a windows NT4 domain to windows 2003. It seems to work well for xp workstations.
I had a problem with all my windows 98 workstations :
Somes, share data with user acces management, and so read the list of permission from my domain.
sometimes (many time in the day in fact) they seems to loose the "contact" with domain controller, and so people who connected to them are asking to put a password (a legal domain user / password) doesn't work.
I saw some article on microsoft support, i follow the instructions but the same.
Thanks for your help