InnerHTML from another page?

hello, I have a question. I would like to know how I can have javascript get the innerHTML from another page's div.

You can open the other page in its own window, or load it in an iframe in the current window document, if both pages are on the same server domain.

You can also get the literal html source of the page with an xmlHttpRequest (AJAX).

ah yeah that's what I was looking for, but I couldn't remember what it was called.

yeah basically I'm trying to get one page to auto-update its contents based on the contents of another page.