Try a really easy to use program like Easeus Partition Master click here. Download and install the Home version, its free. Check how much free space you have on drive before you partition and make partition at least 30% less than free space.
When you say you have free space is that unused space on your C: drive or have you shrunk the C: partition already so that you have unallocated space that you can create your new partition on? You cannot create the new partition on top of he original partition.