It is the
target and
name attributes you will use for this.
<iframe name="auxwin"></iframe>
<a href="scriptingok.com" target="auxwin">This opens in the iframe</a>
<a href=".scriptingok.com" target="_blank">This opens in the a new window</a>
<a href="scriptingok.com" target="auxwin2">This opens in a window called auxwin2</a>
<!--if the window doesnt exist it will create it-->
<a href="scriptingok.com" target="_self">This opens in the the same window (or frame or iframe)</a>
<a href="scriptingok.com" target="_parent">This opens in the window (frame or iframe) that contains your window (frame or iframe)</a>
<a href="scriptingok.com" target="_top">This opens in the "main" window (full screen)</a>