Hello Marcos! It seems your account has been flagged for the forums for a while now, as indicated by the "Twilight Struggle Backer" above and below your profile picture, so you should already have access to the forums here: http://playdek.invisionzone.com/index.php?/forum/92-kickstarter-backers/
Please let me know if you are not able to enter that section.
As for the beta key, that will need to be requested through our support email at firstname.lastname@example.org
Please include the email you used for both Kickstarter and BackerKit (if they are different), and they should be able to set you up with a beta key. Hope that helps!
Also, we have been flagging people periodically in this thread, so if you are curious as to whether you are flagged, if you see "Twilight Struggle Backer" below your profile picture, then you are good to go. The title will change above your profile picture shortly after. You also should have access to the private forums, which is restricted without the forum flagging. If you see the title change around your profile picture and cannot access the forums, please let us know!
However everyone is flagged properly and should be good to go!