For the first part of your query, to make the left column editable:
In your template, select the left column div or area you want to make editable, and in the menu choose:
Insert > Template Objects > Editable Region
Save your template page and it should update your pages to have the new editable region.
For the second part, I'm not sure why there isn't a template showing for those. Site Assist usually creates two templates, - one for the 'Home' page, and another for the content pages. Also you say that these pages don't link to a template', - if that were the case then there should be no problem editing them. Is it possible you deleted one of the templates?
You should still be able to edit them, however. Open one of those pages and in the Dreamweaver Menu choose:
Modify > Templates > Detach from Template.
This should allow you to edit the page. You could then save that page as a template (if you wanted to).
