Dual Boot 2000 and XP – Problems!

Added XP to a system initially setup with 2000.
Both are NTFS. Three drives installed. When
booting to C: with 2000, everything is great,
sees D: and E:; XP boots to D: drive, and sees
E: drive ok, but can’t access C: drive. All
permissions are set to full access for all
users in each boot environment, but even with
full administrator privileges, nothing works to
permit access to the C: drive when booting
from XP. Help!