AD plug-in causing high CPU load on AD

Wondering if anyone else has seen this - we have an AD domain running on Windows Server 2000 (WS2K is actually a hosted OS running in VMWare on top of Linux). All has been fine on the servers for PCs in the domain. I managed to bind Mac OS X 10.3 machines to the domain, but soon afterwards started getting complaints from our AD administrators that they were causing cpu usage "spike" on the AD servers. Whenever a spike would occur, the server's CPU usage would go up to 100% for 20 seconds or so and then drop. This would then repeat every 2 minutes or so. Taking the Macs (and there have never been more than 5 or 6, whereas there are hundreds of PCs in the domain) out of the domain brought cpu usage back to a more normal level. The other thing we noticed is that AD reports that they are "Domain Controllers", not "Computer/Workstation".