The best way to do this would be to create a replica or a DFS on Windows. But that is not by far the most cost effective. If you have a gigabit network and an identical array to mirror that would be great but chances are you are going to be backing up to a LTO3 Tape library using something like Arcserve or Veritas. Each tape can hold about 800gb compressed so you could do it with a single LTO3 drive if you are willing to swap the tapes out.
You can find purchasing options here for the lto3′s.
You can then backup using a differential or full backup and rotate the tapes every so often. It all comes down to what your environment and budget are.