NAME: DiskSize

     USE:  Function to return the amount of used disk space, in bytes,
           of the specified drive.  A numeric value corresponding to
           the desired disk drive is passed to DiskFree, a value of 0
           identifies the default drive, 1 equals drive A, etc.

     DEPENDENCY:  The DOS unit must be used placed in the uses section.

     SYNTAX:  DiskSize(DriveNumber);
              DiskSize(Word);