It is hard for me to visuallize your code so I'm not sure eactly where you would put this...
But where ever you want the person to click you would put
onClick=sendBack(":-)") or whatever string you want sent back to the text area...
Then in the javascript use
function sendBack(myString) {
var txt = opener.document.form1.MMessage.value
opener.document.form1.MMessage.value = txt+myString
}
I haven't tested this but in theory it should work.