Do you need to put any text into your participant notes column, or is it
white space for participants to write in?

If it is just white space, then use Mirror Margins and Different Odd and
Even to get a single 2/3 width text column on the page - i.e. a wide outside
margin for the notes area. In Header and Footer view, insert the page
numbers from the H&F toolbar, and add your grey lines. You can also add any
text that must appear on every page  (for instance, if you had a
"Participant Notes heading, you could put that in a text box anchored to the
header or footer and positioned at the top of the wide margin)

If your participant notes are part of the manual text it is more difficult,
as Word doesn't handle more than one text flow well. Probably the best bet
would be to use text boxes positioned in the "outside margins" set up as
above (use absolute positioning to fix with respect to page or margins), and
anchor each one to the relevant text. If the notes need to flow over more
than one page you can link the text boxes, but there is a limit of 32 boxes
in one flow, IIRC).

An alternative is to use a table (use the full page width in this case, and
two table columns for the two text columns.) You'll need to divide into rows
to align the notes and text, and to prevent the document becoming unstable
(Word doesn't handle rows extending over many pages well). Use the table
borders to place your top grey and vertical lines, with internal row
dividing borders set to None.

Hope this helps