Reinstalling Windows While Keeping Single Folder

I've been having a lot of problems with Windows and my programs. I think it's time for a reinstall. However, I have about 100 GB worth of files I'd like to save and get back after a restore. What would be the best way to go about doing this? Would my files be safe if I stored them on a separate partition on my main hard drive before a restore? I don't have an external hard drive large enough to hold these files during a restore.

from command prompt(admin)

type> diskpart
type> select disk 0
type> list partition

post a pic of diskpart

ok you are booted via Legacy Bios

go into disk management

and shrink C by 131GB or 134144MB

create and format the unallocated space to ntfs and assign a drive letter
Copy your data to the new DATA partition..

insert your setup media, choose custom (clean) install and it should point to your 800GB partition with your preset version of windows, and let setup over write the windows files..

do not delete any of the partitions on that partitions screen just make sure windows is told to install on the 800 GB partition

after setup - you can then copy D to C and delete D and expand C

NOTE: Personally I would shrinke C to around 231GB and leave the rest for DATA 700 GB