PHP Contact Form

I have a contact form that I created on my wordpress blog. It’s a standard form and looks like the following:

<form action="http://www.joelongstreet.com/sendmail.php">
        	<h3>Name:</h3><br />
	        <input type="text" /><br />
    	    <h3>Email:</h3><br />
        	<input type="text" /><br />
	        <h3>Message:</h3><br />
    	    <textarea></textarea><br />
            <input type="image" src="http://www.joelongstreet.com/images/pushMe.png" style="margin-top:6px; border:none; background-color:#eaeaea; width:65px; float:right;" name="submit" value="Submit"/>

I get an error though when my php file is called. How can I get around this without installing a wordpress plugin?

Thanks,

Joe