Any partition software just to partition unused space?
You can use Partition Magic in Windows and divide hard on two virtual hard disks. And then use one for Mac and one for Win.

And for Mac and Win can work at one hard drive, just reformat a hard drive to FAT32.

If you don't want format your hard drive:


Open Partition Magic
Create a second virtual hard drive on free space. Recommended percent: 50% on 50%
Reformat second virtual hard drive to FAT32