XP Clients 100% CPU Usage on W2K Network

I have a W2K Domain with approx 150 workstation (135-W2K Professional, 10-XP Professional).
ALL XP clients show CPU Usage pulsing between 85% and 100% when connected to the network. This behavior is consistent even when the machines are idle and worse when running an app. All XP Clients show normal CPU Usage when disconnected from the network. This behavior is not duplicated on the W2K Clients. All XP\W2K machines have been updated with the latest Service Packs and MS Patches. Has anyone seen this behavior before and if so,what is the solution?

Thanks.