Is it correct to use DIV inside FORM?
It is totally fine .
The form will submit only its input type controls ( *also Textarea , Select , etc...).
You have nothing to worry about a div within a form.
It is completely acceptable to use a DIV inside a <form> tag.
If you look at the default CSS 2.1 stylesheet, div and p are both in the display: block category. Then looking at the HTML 4.01 specification for the form element, they include not only <p> tags, but <table> tags, so of course <div> would meet the same criteria. There is also a <legend> tag inside the form in the documentation.
For instance, the following passes HTML4 validation in strict mode:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<META http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Test</title>
</head>
<body>
<form id="test" action="test.php">
<div>
Test: <input name="blah" value="test" type="text">
</div>
</form>
</body>
</html>