I want to embark on learning a totally new language for web back-end development and I've narrowed down my choice between these three:

GWT 
Ruby
Python

Do you know or recommend of any sites that walks you through building a simple site using these technologies that could be easily deployed and tested?
By the way, I am running a Windows OS, so please let me know if there is anything I may need to configure on my machine to start learning these tools.
On the front end side of development, I would also like to see some samples that greatly exemplifies being able to use the technologies in its full potentials.
Totally appreciate your suggestions and responses. Thank you.
Angelo
@Finbarr...but it contains a full fledged Java Servlet Backend. 
And this is probably why I'd suggest you to use RoR or Django or something too cook up a simple website. 
GWT Applications are usually made of Server components written in Java and Client Side code (mostly JavaScript) that has been generated from Java. Ususally GWT is not what you want for a simple company website.
GWT or Python or Ruby for Web Development