You can download ShowX from the sourceforge page of the project, selecting the last release available. To use ShowX into your solutions, simply reference the main assembly ShowX.dll.
There is also a companion project, The ShowX WebSamples (available from the same page), which is a very easy to install web application that uses ShowX. You may install these samples, and play around to understand how to use ShowX on your solution.
Sooner than later, I'm preparing to launch the first release of the ShowX Web Blocks, a collection of high level web components build on top of ShowX and NHibernate. In the first release, I will include a briefcase and a FAQs web component.