So you can run the widget (double click its file, and it gets added as an active widget in Dashboard), but you can't see it in the dashboard list at the bottom, right? Try "killall Dock" from terminal. After the dock restarts, look in Dashboard.
Sometimes, though, the update of this seems funny. I had a widget called KM-US Doppler, which is an enhanced version of US Doppler. After I installed it, I could launch either version, but only KM showed in the list.

But when I deleted KM-US Doppler and restarted Dashboard, the original US Doppler came back!