html
<input type="submit" id="submit_button" class="push" value="Complete Registration"</input>
js
if (this.checked && $("#num_attendees option:selected").text() != 'Please Choose'
&& $.stepTwoComplete_one == 'complete' && $.stepTwoComplete_two == 'complete') {
$("#submit_button").attr("disabled",false);
} else {
$("#submit_button").attr("disabled",true);
}