OS X can only read NTFS formatted drives. OS X cannot write to NTFS.
My BootCamp / Parallels partition is formatted with FAT32 so I can have read/write access from my Mac.
If you need to write to an NTFS partition, you might find some success dealing with MacFuse. I've not used this and can't make any claims as to its ease of use or quality. See
here for a starting point.