Can I use the free space on an NTFS Hard Drive to make a "Mac OS Journaled" partition to use as a backup space?
If you've already got GParted, use ´GParted /dev/disk1´ to resize your NTFS partition.  It has a nice Graphical front-end, and just in case you need it, here is the manual.
As David Anderson said a couple times, above, then you can open the OSX application Disk Utility, which is under /Applications/Utilities, and then you will see empty space on that disk:
Create a partition of the type HFS+ (journaled), and you'll be ready to use it as your Time Machine disk.


I think you'll be finished in no time, since you personally already found Gparted, and sound like you have good information about this.  You would also be able to do this all on the command-line is OSX with diskutil.