In Windows 2000 you can't change the drive letter for a Boot or System volume using Disk Administrator (on Computer management). But you can change the letter using Regedit.
Start Regedit, go to:
HKEY_LOCAL_MACHINESystemMountedDevices and search for a value named DosDeviceC:. Change the "C:" to a drive letter of your choice.
Restart Windows and Voila! Your C: drive has changed.