The forum post describing how to install the UT pre-alpha playable build is only visible to signed in forum members in the Top Secret Members Only forum. Unreal Tournament is still very early in development, so the build is incomplete, buggy, full of placeholder art and therefore is not in any way representative of the ultimate vision for the game. You really shouldn't play it now! We’ve made it available to Unreal Tournament forum members so they can try the game out and offer constructive feedback on these forums, or maybe even jump in and start contributing.
We put a new build up on 10/10/2014
If you are signed in to the forum, click HERE to go to the Top Secret (shhhhh) post.