<div>'s acting like Iframes?

I have a website where, using div tags I have the content and menu all nicely devided up. My question is what is the best way to change the content of a div tag using a link click from inside another div tag on the same page? e.g using divs instead of iframes

If it's OK to refresh the page, then PHP includes would be the answer.

If it's NOT OK to refresh the page, then PHP and Javascript would be the answer.