I have a domain controller running 2003 R2. The server behaves very well when restarted daily, however, each day it is not restarted, there's a process called "System" that takes enourmous chunks of CPU time (up to 95%).
The server supports AD, WINS, DNS, has Kaspersky Endpoint Security running, and manages backups via Arcserve 15.
When I tried so far: Process Explorer (ex-Sysinternals) shows that the "System" process has no sub-processes. In the "Threads" tab of the detailled view I can see that >90% of the CPU time is used up by "ntkrnlpa.exe+0x803c0". The "Interrupts" process is running at 3-5% of CPU time, I'm not sure if this accounts for the amount of CPU time that System takes.