In Word 2007 and 2010, when you click the Numbering (or Bullets) button, you get the most recent number (bullet) format within the current document and current session of Word. That's the closest you get to a default setting with list formats in Word.
To really get control over numbering, you'll need to set it up using styles. With single-level numbering, you can make use of the built-in List Number style, which can be edited to suit your needs.
For multilevel numbering, see
http://www.shaunakelly.com/word/numb...g20072010.html.