Trying to dynamically add a textbox to a web page

My company uses the jQuery MMenu plugin to add menus to the sites we build.  I've written a wrapper in C# that builds the HTML code to work with this menu.  It works great. Now I'm trying to add a Search textbox.  Here's the portion of HTML code that appears in the layout code:
<li><a href='#'>Find</a><ul><li>Search for: &nbsp; <input class='menuSearch' type='text' id='search' name='search' size='50' value='abc' /><br /></li></ul></li> This code "looks" right but in the menu the "Search for:" appears but not the textbox.  Might anyone know why?  Do I have to add an HTML element in a special way, perhaps with jQuery? Note: For complex technical reasons, I can't add ASP.NET TextBox controls and have to stick to <input type='text'> elements. Robert