Files per volume:
FAT16 = 2^16
FAT32 = 2^32
NTFS = 2^32-1 (that's four billion files)
Files per directory:
FAT16 = 2^16-2 physical directory entries (affected by long filenames)
FAT32 = 2^16-2 physical directory entries (affected by long filenames)
NTFS = No limit