If your Linux distribution has an interface, you can use GParted (Debian based Linux distributions). The application is found in every release as it's a basic program required by the system for partition creation. Simply open the application, and all the hard disks will be listed in the opened window. If you have an empty unallocated space, right click it and select Create Partition. On the next window, choose what File System the partition is going to be, how much space it should take and what it should contain. If you continue to use Linux, make the partition as EXT3 and format it. It should be mounted automatically when the process is finished.
In case you have a KDE environment, the partition editor will look 99 % the same as GParted. The single difference is the layout of the application.