After logging-in with your normal PlayStation (Sony Entertainment) Network user name/password credentials & answering a couple of questions about experience with the “LittleBigPlanet™” & “ModNation™ Racers” franchises you should see the message…
Thank you for showing your interest in the LittleBigPlanet™ Karting PlayStation® 3 Beta. We will be in touch soon if you are successful.
PS. Beta Trial Agreement
[ https://psnbeta.eu.playstation.com/beta_agreement.php ]
“…You must be over 18 years of age to take part in a Beta Trial and, if the Beta Trial takes place via PlayStation© Network (“PSN”), you must be a PSN Master Account Holder….”