I'd suggest using the "id" attribute for the divs instead of class. Anyhow, I'll knock something up if I get home and you haven't figured it out. Basically, you would need to write a JavaScript function that uses GetElementById() or GetElementByObject().
Then define a button that calls that function passing it the id of the div and the id of the textarea. Finally, set the textarea object's value to the div object's value.
EDIT: Here's the function.
<script type="text/javascript">
function copyValues(idFrom, idTo) {
var objFrom = document.getElementById(idFrom);
var objTo = document.getElementById(idTo);
objTo.value = objFrom.value
}
</script>
On the event you want it triggered:
copyValues("div1", "textarea1");
copyValues("div2", "textarea2");
copyValues("div3", "textarea3");