Place the text cursor at the end of the exisiting story (and a paragraph return if there isn't one already or the new text will append to the last paragraph). File > Place and uncheck the replace existing content box.
Thanks, but that's not what I had in mind. There is no existing story. The problem is that I've defined a text frame on the master page but when I place text on page one, using the shift key open to keep adding text until it's all been flowed, ID ignores the master page text frames and just flows the text within the margins of the page, NOT within the text frame I created.
Ah. You're probably clicking on a Guide. Make sure you put the cursor in empty space inside the frame area before you click.
Create a new document with the .75 inch margins but also click "Master Text Frames". I'm also assuming you want facing pages.
Now go to the one master page in the document. Select each of the text frames on the master pages and change the number of columns from 1 to 2.
Now go back to the first page. Go load the cursor with the text.
Place the cursor inside where the text frame is. You will see the cursor straight lines become curved. That indicates that you're about to put the text into the master text frame (even though it's not selected).
Now hold the Shift key. The cursor will change to an arrow that goes up and down. This indicates the autoflow to all the pages.
You should now have all the pages you want.