Oh, sure. You're talking about a classical backup application. Again, I'm compelled to mention one of my employer's products... Norton Ghost. It can back up to your Buffalo network attached storage device, can be set to run on a scheduled basis, and can use disk imaging to create a backup that will recover everything on your PC in one step. I can get it for you for $15, if you like.

Another popular choice: Acronis True Image. But there are literally hundreds of backup applications, of varying degrees of reliability and usability. There's a good chance that the Buffalo device came with something, or that some other bit of hardware came with a backup app.