Making 7 Seater Cars Future Proof

I am in the process of trying to make my website on 7 Seater Cars: www.7-seater-cars.co.uk future proof.  I am developing the site for Mobile Phones so that it can be viewed on any high end devices such as the Iphone, HTC or Blackberry.  This involves re-writing the PHP code into narrower pixels that are easier to read on smaller screens.  Although the site can easily be viewed on my HTC Hero phone it still involves a lot of scrolling across.  So the new Mobile PHP site will be a narrower version of the current site.

I am also cleaning all the HTML/PHP code so that it is 100% Validated with the Markup Validation Service.  This is quite easy on the main site because I have control over all the code.  However as soon as a YouTube Video is embedded or a Subscriber form from Google is included there are errors.