In Windows 2000 and XP Performance Monitor disk counters for physical disks are turned on by default, disk counters for logical disks are turned off by default.

You can disable all disk monitoring by running this command

DISKPERF -N

To turn it on again run this command

DISKPERF -YD

all DISKPERF switches:
   -Y  Sets the system to start all disk performance counters
       when you restart the computer.
   -YD Enables the disk performance counters for physical drives when you
       restart the computer.
   -YV Enables the disk performance counters for logical drives
       or storage volumes when you restart the computer.
   -N  Sets the system to disable all disk performance counters when you
       restart the computer.
   -ND Disables the disk performance counters for physical drives.
   -NV Disables the disk performance counters for logical drives.