You don't tell us where to put the text box or what to put in it.
I took the language="javascript" out of your script tag, it's not needed.
I added a second set of td's to the last row of the table as per table rules(?)
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/javascript">
function create() {
var box = document.createElement("input");
document.body.appendChild(box);
}
</script>
</head>
<body>
<table>
<tr>
<td><label for="ctrlname"> Createcontrol*</label></td>
<td><input type="text" id ="Text1" name="Createcontrol" maxlength="50" size="30"/></td>
</tr>
<tr>
<td><label for="quantity"> quantity*</label></td>
<td><input type="text" id ="Text2" name="quantity" maxlength="50" size="30"/></td>
</tr>
<tr>
<td><input type="button" id ="btncr" value= "create" onclick="create()"/></td>
<td></td>
</tr>
</table>
</body>
</html>