Uh, InDesign is print only. You'll be looking at Dreamweaver for web. TBH, I don't bother though - I just edit the CSS and see how it comes out.

Also, generally, you need not bother with XML, or PHP or anything like that. A Content Management System like Wordpress, Joomla or Drupal will handle all that for you - you just concentrate on the CSS in the theme.