Using Time Machine with a already used NTFS disk
Time Machine requires an HFS+ partition on the drive, it can't use an NTFS formatted one, even with MacFUSE installed. The way to do this would be to shrink the NTFS partition, then make a new HFS+ formatted partition to use with Time Machine (you can do this with Disk Utility). Unfortunately OS X can't resize NTFS partitions, you'll need to use a Windows machine to do it, then use OS X to create a new HFS+ partition.