I am using OpenOffice Writer 2.0.1 and wish get step-by-step
instructions for using a style to get a document that reads like this:

1.0  _My First Section_

<stuff>

1.1  _My First SubSection_

<more stuff>

1.2  _My Second SubSection_

<more stuff>

2.0 _My Second Section_

<even more stuff>


In particular, I want the ".0" to appear in the "Heading 1" style. 
This, for example, is inadequte:

1. _My First Section_

1.1 _My First Sub Section_ 


Additionally:

- The ".0" must also appear in the table of contents.
- If I insert a new Heading 1 line, then everything below it increments.

Does page 67 of the guide answer this...ie...do it once and make it a
custome style?

http://documentation.openoffice.org/manuals/OOo2.x/user_guide2_draft.pdf

No, this documentation is inappropriate.

In Microsoft Word, if you right-click a heading, then you can get the
desired behavior by choosing "Continue Numbering" or "Stop Numbering"
from the context menu.