There is a few things that needs to happen to get this working correctly:
1. first remove the input field and captcha image in Dreamweaver (you can use design view)
2. you will need to remove the spry validation at the bottom of the page:
var sprytextfield9 = new Spry.Widget.ValidationTextField("sprytextfield9", "none", {minChars:5, maxChars:5, validateOn:["blur"]});
3. remove the server side validation at the top of the page:
$WAFV_Errors .= WAValidateLE(((isset($_POST["Security_code"]))?strtolower($_POST["Security_code"]):"") . "",((isset($_SESSION["captcha_1"]))?strtolower($_SESSION["captcha_1"]):"") . "",true,7);
This should remove the captcha.