Dralzz

I had the same problem, and thought I had uninstalled the demo from my computer. However, because it's so bothersome to find the "Uninstall programs" menu in Vista, I just delete things. I uninstalled the demo the proper way, and then I was able to install the game.

Congrats! Now just hope you're able to install it. The game appears pretty hit-and-miss on that topic.