If you don't need a Mac formatted drive anymore then it may be possible to delete the existing partition using Windows Computer Management > Storage and create new NTFS volume, and format it as a logical drive. Got any details on the model of drive? If it's a standard USB or Firewire connection I don't see any problem with the above. If it fails due to some weird interface compatibility issue then you can always reformat it as a Mac drive. Of course you do know that reformatting will erase any data on the drive?