Add another drive and install the programs there. Or, did you say you already have an empty disk there? Almost every program has the ability to modify the address where it will be installed. You can also address your downloads, photos and other space consuming folders to that storage drive.
That will mean that you'd have Windows on your C:\ drive and maybe some programs/games you want to load fast - unless you get an SSD for storage - and most of your games and other stuff on D:\ or E:\ or whichever letter you have available.
No matter which drive you install your software on, there'll usually be some instructive files on C, most likely in a hidden folder so you won't mess with them. But they're not too big to worry about. For best performance it has been good practice to have the C:\ (System) drive only half filled for temporary data. Current drives can be so large that having half of that unused most likely is overkill. But some 30GB of free space there won't hurt and more is more.
