Slow logon in W2k AD Domain

I have created a test Windows 2000 AD Domain. The problem I am having is when I change the domain membership of a pc it takes up to 40 minutes for the pc/user to logon to the AD domain. It makes no difference to the logon time if I apply a group policy or not. The only way around it that I have found is to re-install the OS ( W2k Pro ) and join the AD domain as part of the install.
Is there an easier way to get around this problem? I have 150 pc’s to move to the new AD domain.