How can I make a search form that can search taxonomies and posts?

Question

I have a search bar on the homepage of my theme. I want the user to be able to select from a drop down to search for everything, posts, or taxonomies. I looked at the wp_dropdown function, but its meant for searching under a single tag, and not within a taxonomie group.

now I just have a html dropdown next to the search form. how can I use the selection from the dropdown to modify the search?

Heres the code im working with

<form class="searchform" method="get" action="#">
        <fieldset>
            <legend class="hidden">Search form</legend>
            <div class="input-holder">
                <input class="search" name="s" type="text" value="Search Here"/>
            </div>
            <select name="cat" id="cat" class="postform" style="display: none; ">
                <option value="0" selected="selected">Everything</option>
                <option class="level-0" value="1">People</option>
                <option class="level-0" value="2">Schools</option>
            </select>
            <button value="submit" class="searchBtn"><span class="hidden">Submit</span></button>
            <!--END #searchform-->
        </fieldset>
    </form>

Answer 1

I believe something like this would do the trick.

EDIT

My code assumes the querystring value is the post_type, not an integer like your form field. Also, your form field is named 'cat', I think WordPress has that reserved, at least I remember having conflicts when I last used 'cat' in a querystring.

EDIT 2

(Changed filter from 'posts_where' to 'pre_get_posts' after having done some tests)

In functions.php

 function my_filter( $query )
 {
      if( is_search() )
      {
           $type = ( !empty( $_GET['your-field'] ) ) ? $_GET['your-field'] : "";

           if( $type )
                $query->set( 'post_type', $type );
      }
 }
 add_filter( 'pre_get_posts', 'my_filter' );