Place the code to the head of the page that has your stream code on it.

Rats. I forgot how I set this up. The Iframe links to my Stream at .coffeecup.com.
Is there anyway to edit the link in the Stream's post box, or add that to the code for just that post?

There maybe a jquery solution for fixing this but the easiest way would be to paste your stream code to a new html page that has this code in the head area then load it with the iframe.
<base target="_blank" />

I remember now why I set it up this way. When it was on a page within my site and I linked the Iframe to it, things on the VSD page (with the Iframe) disappeared. I just couldn't get it to work at all so I linked directly to my Stream instead.

Here's the link I want to change:
<p>You can get a free sample (or purchase it) at his site: <a href="http://boagworld.com/books/">http://boagworld.com/books/</a></p>

That's from the Stream > Edit Post > Source

Editing a post is simple. I thought you were looking to edit the stream generated code.