Kelmel, you can use an NTFS formatted disk in both operating systems, but OS X can only read an NTFS disk, not write to it. I would recommend formatting the 3rd and 4th disks in FAT32 so you can have read/write abilities in both OSes. The only drawback of FAT32 is there is a limit on individual file sizes; I believe it is 4GB, which may be a problem if you do video editing (plus it's an old file system). Alternatively, what I did with my 320 gig external drive is make three partitions so I can use native file systems for each operating system: one in the Mac OS Extended format (HFS+, non-journaled), one in NTFS, and one in FAT32. That way, I can use native file systems for both OSes and use the FAT32 space to transfer between them (i.e. a temp space). Windows will not see your Mac partition at all, but you can still copy files from the NTFS partition to the HFS+ Mac partition with OS X. Good luck on your Mac Pro purchase, the new octo-core setups look INSANE!