You could use the Disk Management to shrink your partition D to get some unalloacted space then create the new partition on it.
Note: because you have three primary partition already ( C drive,D drive and an hidden drive "system reseverd" which is contain the boot file of the Windows 7) , when you create the fourth partition the partition will be default as "extended partition" therefore you could only create logical partition by shrink this "extended partition" if you shrink the primary partition you can not create any partition. This is because the system could only allow 4 partitions, three primary partition with one Extend partition
You could choose other partition software to help you create partition which has the option to choice "primary partition" or "logical partition"
you could learn how to create partition from http://www.partition-magic.org/help/create-partition.ht...