Slow restart/log off when on a domain

Dell gx50, 1.2 mhz, windows 2000, it works fine and fast, but when I join the windows 2000 domain, theses computers become slow to restart, shut dowm or even loging off the user. This seems to be commmon to all of theses machines. We are on 100 Mbpsnetwork and there are no problems with network performance, everything else is fine. Any ideias?

Thanks,

Romulo