In order to partition a hard disk, go to "Control Panel", "Administrative Tools", "Computer Management", "System Tools", "Storage", and then "Disk Management". Right click on the unallocated disk area and follow the partitioning wizard.
I usually make a C partition of about 100 gig and put all my data on the D partition when I have a computer with a single hard disk. Otherwise, I use a small hard disk as a C drive containing the OS and install a large hard disk as a D drive for data. The big advantage of partitions is that you can re-install the OS without loosing your data.