An Improved Tutorial for Expanding Joomla Themes
First of all, I fixed the Joomla feature in psd2css Online to not allow your content to go flowing out of your design by default. Until yesterday, if you made a nice 900 pixel tall Joomla Template for example, but your content was 3000 pixels high, it would just flow out of your design and look terrible. The only option at that point was the Expanding Template trick that I have a couple of videos about here. But that's complicated and now might not even be necessary. Try your design again on psd2css Online and see if the new way content stays confined to the content area is good for you.
BUT - if it's not :) Then you still probably want to do the Expanding Template technique. Here is an improved tutorial/example for how to do that. In this example we have a video tutorial, we have a live website that uses the technique, and at the website we have a much more indepth text description of exactly how to do the Expanding Template technique. The example uses Joomla, but the technique is the same for Drupal and WordPress templates.
Here is the live site: http://jexpand.psd2cssonline.com