Add html elements to your form to hold the content that you want to show with colorbox. Put each one in it's own html element. Then preview your form and look at the source code. Make a note of the ID of the div that holds all the content for each html element. They should be something like item1 or item5 etc. Add a dropdown to your form and name the options. Next paste this code below into a html element and adjust the item, the select name and the option value to those used in your form. If you need more then six add more else if statements to meet the additional html elements and their ID's.

Google colorbox and download the needed files. Upload those to your host and adjust the script links to those files.

<link rel="stylesheet" href="http://mydomain/colorbox/colorbox.css" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script src="http://mydomain/colorbox/jquery.colorbox.js"></script>
<script>
var jQ = $.noConflict();
jQ(document).ready(function() {
jQ("#item5").css("display", "none");
jQ("#item6").css("display", "none");
jQ("#item7").css("display", "none");
jQ("#item11").css("display", "none");
jQ("#item12").css("display", "none");
jQ("#item13").css("display", "none");

jQ("select[name='poem_select1'],select[name='poem_select2").change(function() {

var currentPoem = jQ(this).val(); // Grab select value :
if( currentPoem == "Poem 1"){
var showPoem = "item5";
jQ("#item5").css("display", "block");
}else if( currentPoem == "Poem 2"){
var showPoem = "item6";
jQ("#item6").css("display", "block");
}else if( currentPoem == "Poem 3"){
var showPoem = "item7";
jQ("#item7").css("display", "block");
}else if( currentPoem == "Poem A"){
var showPoem = "item11";
jQ("#item11").css("display", "block");
}else if( currentPoem == "Poem B"){
var showPoem = "item12";
jQ("#item12").css("display", "block");
}else if( currentPoem == "Poem C"){
var showPoem = "item13";
jQ("#item13").css("display", "block");
}
var cboxOptions = {
width: '95%',
height: '95%',
maxWidth: '400px',
maxHeight: '400px',
inline: true,
href:"#" + showPoem + "",
}

jQ.colorbox({
width: cboxOptions.width,
height: cboxOptions.height,
maxWidth: cboxOptions.maxWidth,
maxHeight: cboxOptions.maxHeight,
inline:cboxOptions.inline,
href:cboxOptions.href,
onClosed:function(){
jQ(cboxOptions.href).css("display", "none");
}
});


jQ(window).on('resize', function(){
jQ.colorbox({
inline:cboxOptions.inline,
href:cboxOptions.href,
width: window.innerWidth > parseInt(cboxOptions.maxWidth) ? cboxOptions.maxWidth : cboxOptions.width,
height: window.innerHeight > parseInt(cboxOptions.maxHeight) ? cboxOptions.maxHeight : cboxOptions.height,
onClosed:function(){
jQ(cboxOptions.href).css("display", "none");
}
});
});

});


});</script>