Do you have to be rooted to get that widget?
You'll need to find the .apk files for the three. It should be someplace over at XDA. From there make sure you have unknown sources checked and use a file explorer (like ES, Astro, or stock) find the .apk files and just install them.
Everything is uninstallable if you don't like it. Unless you have a motorola phone. In that case only the launcher and widget are uninstallable. The weather app will replace your current one. So, you may want to make a backup of your current weather app.