A very useful feature in Microsoft Office is called "AutoRecover", which automatically saves your document at specified time intervals so that in case of an application or system crash, Office can recover its latest version.
By default this is set to 10 minutes, but you can change this easily by clicking on the Office button within the application, and then clicking on the "Word Options" or "Excel Options" (or other application) button in the lower right hand side of the window. Go to the "Save" section and look for "Save AutoRecover information every…" and change the settings there. Be sure to click "OK" to save your preference. A word of caution: setting the interval at very short timespans such as every 1 minute can slow down your computer with frequent writes to the hard disk. Try a number between 5 minutes to 10 minutes first.