XP Slow with AD

We recently converted to W2K server with Active Directory. So far everything is fine except for the two workstations running XP Professional (all the rest are running 2000 Pro). Those two are unbearably slow when connecting to any networked resource, such as mapped drives, printers, shared folders, etc. Access to the local machine is fine. I have a feeling something needs to be tweaked in Active Directory, or perhaps the registry that is XP specific. Any ideas?