To access beta versions of ADOM you need to take the following steps:
- Start Steam and log in.
- Go to your games library.
- Right-click on the ADOM entry.
- Select the bottom entry of the context menu ("Eigenschaften" in Germany, probably something like "Properties" in English, etc.).
- Go to the "Betas" tab in the properties window.
- Select "beta - Public beta test" as the game version you want to use.
- Close the window with the button in the bottom right corner.
- Start ADOM - the beta version will be downloaded and ready for play.
Please remember to switch back to the stable branch when you are done with beta testing!