I have done it before. It was on my remaining Windows machine which is running xp. This is the procedure that I used.

The first thing that I did was to clean the disk to get rid of temporary files and cache.

The second thing was to defrag the disk with Auslogics Disk Defrag. It has a function to optimize the disk for fast operation. Part of that process is arranging files so that, where possible, entire programs are organized in a single place on the drive. This function takes longer than a normal defrag so allow time for the process. As a result your data is arranged toward the beginning of the drive, freeing up more room for the new partition. download Auslogics Disk Drfrag.

Then I used partitioning software to create the new partition.