You could use Mac Drive if you want to pay $50 to let windows read HFS+
OR you can do it the other way. .
Partitioning will erase ALL data on the drive. Make sure everything is backed up before Proceeding!!!
Enter Disk Utility
applications/Urilities/Disk Utility.app
FAT32/HFS+J
Select the External Drive, and click on the "Partition" tab. You will see a display on the left of the drive, and how many partitions or sections it has (which will be one solid block).
Click on "Split" below the the display, and select a size for the new partition. If you make it 100GB, the display will then show 2 blocks, one small, and one taking up the rest of the space on the drive.
Click on the small block to select it, and select from the "Format" dropdown list on the right: "MS-DOS File System". There 5 buttons at the bottom "Split" "delete" "options" "revert" & "partition".
Select "Options" and choose "Master Boot Record". Now that that part is setup, select the larger block. Repeat the same processes, but choose "HFS+J" from the dropdown list, and "GUID" from the "options" menu. (GUID is If you use intel mac, otherwise use "Apple partition".)
To format NTFS. .
Partition in Disk Utility like above, and hook it to a windows machine. The FAT32 partition should come up as if it is an external HDD that is only 100GB in size (windows won't be able to read the other 400GB). Right click the drive, and select "Format". It should give an option for NTFS.
Once windows is done, that small partition will be NTFS, and easily be read by windows whenever you plug it in. OS X can only Read NTFS out of the box, you'll need third party software as I stated earlier to read & write to NTFS.