Try going to the Big Fish site at http://www.bigfishgames.com/download-games/1420/virtualvillagersth/index.html and downloading the trial (click the Download button). After installing the new version you may then need to enter your name and unlock key again. It is possible that it may no longer work as I believe BFG have changed their system since. In that case I suggest you check their help - you'd probably need to contact them to get a new key.