Thanks, but I have to confess that I missed a couple of points :*)
This workaround is straightforward, but this is the first time I've outlined it in a forum post so please forgive the omissions. I'll look at gathering it into a help document when I have the time. Moving on...
The form must post to itself
Open your index.php file, and change the action value on the form tag from contact.php to index.php
Fixing the validation message
Open sc_admin/includes/contact/posted.php
Find where it says Please enter your company and replace it with Please enter your birth date. This makes the form show an appropriate message if the user doesn't complete the field.
Styling the form
I can see by viewing the source of your index.php page that you are familiar with CSS. I forgot to mention that you need to paste a link to simpleContact's CSS file into your head.
Open contact.php and look in the head. Find where it says:
<link rel="stylesheet" type="text/css" media="screen" href="screen.css" />
Paste that into your index.php before the closing </head> tag. Make sure that the CSS file is uploaded.
You will probably want to remove the CSS instructions that are making the form background white. Since you're using a blue background I'd recommend making the labels white and the error messages yellow (removing the arrows too).
You can now remove contact.php from your web server - you don't need it.
Hope this helps.