Using network hard drive for backup
It depends what sort of backup you want to do. If you’re happy just backing up regular files, then there are a bazillion (really, that many!) different bits of freeware to do that. There is a good list here:
Download Back Up Tools for Windows – MajorGeeks
and pretty much all of them can do network backups. Some even have fancy options like encryption. Really, the most useful thing is just being able to schedule them and know they ran OK.
You may also want to make a system image backup too, and you’ll find that software in the very same list.
I don’t have Windows 8 as yet, so I’m afraid I can’t suggest any for that platform. Personally, I use Clonezilla for image backups.