Hey Andy,
I think it would a bit overkill to backup all files on your harddisk. It takes a whole lot of time and even before you have finished the backup, som files would be outdate. And if you have a disk error of some kind. In most cases a restore of an backup isn't enought. So I would backup things of value to you. the documents and settings folder is a good one, if you have any fs addons in download form then back them up too. Look at your harddisk and ask you self. If lost all this today, what do I have here that I need to save because I don't have on cd or dvd.