This modules enables the split testing of two Drupal themes. Each alternating anonymous visitor to the site is assigned a different theme, and if the user reaches the action page (such as a thankyou page) the conversion is recorded. The split test ends when the total number of visitors to test, is reached.
Also see Multivariate module
Sam Hassell of Webzen. The author can also be contacted for paid customizations of this module as well as Drupal consulting, installation, development, and customizations.