This a very basic example, on how to have your 2 forms in one. The JavaScript will just show the comment form when the user clicks on "Search".
<!DOCTYPE html>
<html>
<head>
<style>
#hiddenStuff {
display: none;
}
</style>
</head>
<body>
<form action="...">
// search fields here
<input type="button" value="Search" onclick="document.getElementById('hiddenStuff').style.display='block';">
<div id="hiddenStuff">
// comment form stuff here
<input type="submit" value="Submit">
</div>
</form>
</body>
</html>
I also made a fiddle, if you want to see the result in action.
Sorry I'm not familiar with ColdFusion, but it shouldn't be too hard for you to translate :)