[SOLVED] Sidebar only on a certain partent page and sub pages

I would like to have the same menu bar on the left side of a set of pages, but those pages will only be identified by their parent page.

For example:

(these are area all on the main menu at the top of the page).
1. Home
2. Project A
3. Project B
4. About
5. Contact

However, on all of the pages that are nested under "Project A" I want to have a left sidebar that is visible on all pages where "Project A" is the parent or grandparent of that page.

Thanks,