|It does not matter which partition a program is installed on.|
You need 20% free space for it to work properly so that is fine.
You have two problems that are making your system 'work overtime' that typically can hog CPU processing power, memory usage, and possibly hard drive transfer bandwidth.
The first common problem is an excess of programs running in the background which you should identify and disable. The second is that Norton 360 itself is a system hog and can overwork and slow down a system.
For the first, uninstall programs that may have some with the system or you installed on a whim but never use. Then use Task Manager or Process Explorer (download from Microsoft) to identify processes running in order to remove them from starting with windows, then run msconfig (type msconfig.exe in run box or msconfig in windows search and select), go to Start tab and uncheck those processes or just uncheck all except mocrosoft and your antivirus program (you can add anything back later), Apply, and restart the machine.
For the second, consider replacing Norton with a better antivirus program that will be much easier on your system and protect it better at the same time. Consider Avast (free version) antivirus that is very highly recommended here (I have used it on a number of machines) as a better alternative, or Webroot (my personal preference, but free trial only) which has a new version recently out which is even better than what I have used for years.
Edit: I did not know that about those other '360's, I just assumed it was Norton 360. I guess this could be much worse. I guess they are preying on those looking for a free version of the popular Norton....
You have to be a little bit crazy to keep you from going insane.