What is the easiest way to create a mobile stylesheet for a Drupal 6 site? Is there a simple way to just create a css file, declare it in the info file add a viewport meta tag to your templates and have it all be automatically recognized by the site pages? Based on my own attempts, I'm thinking it's a little more complicated than that, but maybe someone has a fairly simple solution...?
Take a look at the Omega base theme. I haven't used this with D6, but the D7 version handles all of the media queries and makes it pretty easy to customize them via the UI settings page.
There are modules like mobile_tools(http://drupal.org/project/mobile_tools) and mobile plugin(http://drupal.org/project/mobileplugin) that have preconfigured themes you could tweak those.If you want to configure/make a mobile theme MOBILE PLUGIN is quite useful. http://drupal.org/node/1008582 follow this link for details of making zen subtheme.
There are several modules which can help you achieve vasts amounts of media detection. Most come with the option to then customize the called stylesheet so you can edit it to your hearts content.