How do I switch out contents of one frame?

I'm making a web site with an expandable menu in the left frame and the usual crap in the right frame. How do I switch out the contents of the right frame *only* whenever a menu option is clicked?

Right now, a menu option calls a dupe of the home page (only with new text in the right frame). It works just fine but I'm calling a new menu as well, and when I do, it reinitializes to a closed state.

If I could switch out just the contents of the right frame, the menu (being untouched) would remain expanded and users would be able to see the list of sup-topics at all times.

Thanks - rev

Found it.

Assume you have two frames on the home page, A containing the menu, B being the content frame.

In frame B you place an iframe statement, something like this:
<iframe name="FRAME2" width="681" height="575" scrolling="yes" frameborder="0" src="intro.html"></iframe>

Assume you have two different pages of content.

src="intro.html" specifies the initial content displayed when the Home page is opened.

When you want to switch out the content of frame B, you add target= to your menu link code in frame A. i.e.

<a href="new_content.html" target="FRAMEB">New Page</a>

When the menu link is clicked, the new content is displayed in frame B.