How many partitions now exist on the hard drive in question? If four, then some rearranging following backup is in order. If three, then things are easier. In either case, do a backup first.
Assuming the latter, first shrink the D:\ by approximately 30 GB using Windows. Then use gparted (it is present in System Rescue CD
) to add another partition. Suggest using FAT32 file system should you want to also see files in Windows.