Regular expression - injecting wrapping div, then removing later

 Hi all,
 I'm having trouble trying to figure out the best approach to this problem and I believe regular expressions are the way to go.
Basically I have created a large string of XHTML using a WYSIWYG editor,
so the string is like "<p>dfdsfjhds <img src='temp.jpg' />
dsfdsfsd</p><p>dfsdfsdfsd</p> ... "



What I want to do is the following...



When SAVING the string to the database I want to replace:



<img class="tmceImg" alt="" src="image.jpg" />



with...



<div class="cnt_tmceImg_left">

 <div class="inner">

   <img class="tmceImg" alt="" src="image.jpg" />

   <p class="sub_text detail">my picture</p>

 </div>

</div>





...