We have recently completed a Drupal 6 project that involved transferring an existing site to the Drupal platform. Introducing, Bushmeat.org. This site is operated by the Bushmeat Crisis Task Force (BCTF), an affiliate of Conservation International and was built using components from the Plumtree system. BCTF wanted to upgrade the look and feel of the site while keeping the navigation and content the same to help accommodate current users.
The main challenge this type of project faced was content material. Where and how to get text, images and downloadable files, from one site to the next was a struggle. The current architecture stored files in multiple folders but only certain content could be downloaded / exported to CSV type document. This meant that any content that was not downloadable had to be re-created manually on the new site.