Resizing mac partition on a volume with boot-camp
For all my partitioning, I use and recommend iPartition.

With its intuitive yet powerful user interface, iPartition makes it easy to create, destroy, resize or format partitions on your hard disks, whether internal, external, fixed or removable.

iPartition even allows you to modify Boot Camp partitions without any problems. iPartition will reconfigure the Windows partitions automatically.

You can use iPartition on drives that contain Boot Camp volumes; in fact, you can even resize your Windows partitions, and let iPartition take care of reconfiguring the Windows boot process for you.