Say No to IE6 the Drupal Way
There's just so much great stuff going on with modern browsers, mobile devices and HTML5, so how does the Drupal community our our best to help innovation by encouraging IE6 users to upgrade to a modern browsing experience. Now Drupal 7 (core) is still will be providing support for IE6, but we really don't want to have to support it for Drupal 8 (which could well be released before IE6 is finally laid to rest by Microsoft). I've written a short note that we're using for our visitors to give them the tools that they need to finally make the move. However, I thought I should document a nice way to do this in Drupal 7. Much of this will be the same for Drupal 6.
Now there are ways to do browser detection with jQuery or other tools, but for Drupal 7 the easiest way seems to be to add a conditional CSS file to the header through the template.php file. The conditional statements work fine for IE 6 & 7, so they do the trick nicely:

We've made a team decision to proactively advocate for people to upgrade from IE6 to a more modern web browser. We're doing this primarily because it has given designers & developers such grief, but also because we want our users to have the best, most secure browsing experience they can.