If you just want to quickly filter the results of an existing report, type "C:" (without the quotes) in the filter box under the Caption column title.
For the reports that show the drive letters, such as "Disk: Servers less than 1 GB free HD", most of them will involve tblDiskdrives. Add to the WHERE clause on the report:
WHERE
condition
AND another_condition
AND tblDiskdrives.Caption = 'C:'
As far as
tblEncryptableVolume goes, the field
DriveLetter contains the drive letter in the form "X:". When you create a report that joins tblEncryptableVolume, you'll want to include
AND tblEncryptableVolume.DriveLetter = 'C:'
in your WHERE clause to filter the results for C: drive.
Refer to
SQL comparison operators and
SQL LIKE operator for information on how to do text string comparisons.