First off, FB is great.
I want to open up an iframe after I hit the submit button on a form. The page that opens in FB needs to be from the form's action when I post.

Any suggestions or direction would be appreciated.

It's not clear to me whether in your case the content of the FB'd page depends on the form's values or not.

You could take a look at the "Talkin' to an iFrame" example right at the bottom of my demo page to see an example of a mini-form that invokes iframed floatbox content. In this case, the loaded page is reaching back to the top document to read the form fields and construct itself accordingly. It's all client side and there is no form post to the server involved.

If it must be server-side code (e.g., you need to capture the form data in logs or tables) your best bet might be to return a page from the post that includes an anchor with the autoStart:true option set on it.