check iframe content from php

Hi ...

I want to make a script to check the content of a iframe included page if it contains blablabla then a link should be activated.

let me explain mare

here is an example page http://myegy.com/test/1/index.php

in the middle of the page thier is a iframe page telling you to submit (some informations for example) and at the end of the page thier is a Link

after you press submit it say thank you
i want to modify the Link's code to be disabled and if the ifame page say thank you then it will be activated.

I wish you could help me and thank you ...

*here is the simple index code

<? include("header.htm"); ?>

<? echo '<p align="center"><iframe src="included.htm"></iframe></p>'; ?>

<? include("footer.htm"); ?>