Make sure you backup you may lose data doing partitions
Download EaseUS home edition:http://www.partition-tool.com/landing/home-download.htm
Install, open program, click on Go to Main Screen. Once you get there, Right click on the drive that you want to split on the bottom half of the screen. And click on Resize partition, so you can drag it to have less space on your hard drive. Then you will have unallocated space. Right click on the unallocated space and you can then right click convert to Primary and format it to NTFS or whatever format your original hard drive uses such as FAT32 or FAT16.
Let me know how it worked out.