Steps:
- Use iPartition, reduce existing HFS+ partition to half-size.
- Don’t create the other partition yet.
- Change Partition-Scheme (from GPT) to MBR
- Otherwise the partition won’t be visible to windows.
- Now create the other partition, e.g. NTFS.
- That option only became available once the partition scheme had been changed.
- Result: [ MBR | HFS+ | NTFS ]