UserCP > Arcade Options.

[z3usX5]

You will see there is a whole new side of the arcade in your User Control Panel under the Arcade Options menu. You can enable Challenges & choose how you are notified. I would recomend that you enable these and let the games begin.
:rock:

Here is a link to the Options.
http://www.nitroaddicts.com/forums/profile.php?do=editarcade