I haven't tried it but, how about opening a word doc (2010) goto Home-> turn on numbering, then select the numbering format you want. Save it as a template. Then use that template as the one you call from automation.
Hopefully everything entered will get automatically numbered.
Other Info:
Walkthrough: Using Automation to Write a Letter in Microsoft Office Word
msdn.microsoft.com/.../dd301252(v=nav.70).aspx
How To Use Automation to Run a Word Macro with Arguments
support.microsoft.com/.../183369
How to create a bulleted or numbered list in Word