The second rule is that good enough is a very important concept. Remember, it's only a thesis. Think of it as a set of smaller, self-contained chunks, and keep each chunk in a separate file. For instance, if you call your main file mythesis.doc you won't have a clue what is in it after a few weeks. The probability of a crash is directly proportional to the importance of the material on it.
Floppy disks are probably a much safer option.
Use one floppy for each chapter. It's important that you don't underestimate how long it will take to write up your final thesis. You will need to produce at least two full versions of the thesis - a first draft version, and a final version which is the one that you submit. In practice, most people don't manage a thousand words a day. A more realistic target is probably something like 2500 words a week, but you will need to make time and space in order to keep to this sort of schedule.