Trying to execute an external php file

OK so I am trying to run this code in my wordpress post:

<div class="div_name">
					<table height="200px">
						<tr><td>
							<form action="" method="post" name="f1">
								<fieldset>
									<legend>Blog Topic Generator</legend>
									<label for="category">Category : </label>
									<select name="category">
										<option value="1">All</option>
										<option value="3">Opinion</option>
										<option value="4">Health</option>
										<option value="5">Religion</option>
										<option value="6">Science</option>
										<option value="7">Art</option>
										<option value="8">World</option>
										<option value="9">Music</option>
										<option value="10">Business</option>
										<option value="11">Personal</option>
										<option value="12">Technology</option>
										<option value="13">People</option>
										<option value="14">Recreation</option>
									</select>
									<input type="button" name="submit" value="Generate Topic"  onclick="JavaScript:xmlhttpPost('ajax.php');" />
								</fieldset>
							</form>
							<br /><br /> 

							<div id="phrase-result"></div>

Code (markup):

I am not a programmer so I am not sure if i am using PHP, Javascript or both? I have the external ajax.php placed in my root directory. I installed this plugin: http://wordpress.org/extend/plugins/exec-php/ which is supposed to allow me to execute php ... but I think it is only for inline php. How do i get my WP blog to execute the external JS that I have?

Thanks ahead!

 

Hey,
To include javascript you need to put something like this in between your head tags

<script type="text/javascript" src="./js/jquery-1.2.6.min.js"></script>

PHP: