I also agree with #10
"MiniPartitionTool" (free Windows software) does an excellent job shrinking/growing Windows partition[s]. It doesn't come bloated with garbage you don't want or malware. Use it to do what you want to get some free space, then reboot to make sure Windows OS runs, shutdown and then do your side-by-side linux install. It's specifically designed to handle Windows partitions. I prefer to use these when dealing with Windows, then GParted after Linux is installed.
GParted is linux software that can also do the job, need a bootable GParted DVD or USB - it is software that will show the partitions on all drives in the machine and allow you to manipulate those partitions (grow, shrink, etc) - it needs you to input the actual dimensions (start and end in bytes or bits) so you will need to do the math.
PartitionWizard is more user-friendly in its GUI's for understanding what you are doing to your Windows partition(s) if you are unfamiliar with Linux and GParted.