Here are some tips that may help you:
1.) You should understand that a valid email address is required and will verified before you can complete your registration.
2.) If you get kicked back to the "fill in details" screen instead of being accepted, pay particular attention and read every note, particularity the one that explains what the problem is.
3.) Note PINK form areas. The color indicates there is something wrong with your entry.
4.) CAPTCHA: If you have any trouble (I did) have the forum play the sound for you. If necessary (and you use Windows) ask it to play it with WMP (I had to).
5.) Passwords: You cannot have your username in your password. You must have both upper case and lower case letters. I suggest a few numbers or special characters would be a good idea.
6.) This part annoys me too. I can't get the CAPTCHA to change or the verification questions to change no matter what I tried. It's not supposed to work that way. (Refreshing the page should fix all that.) If all else fails, close your browser then restart and begin registration again.
I apologize for any problems in the process. Spammers make it necessary to have registration systems that are somewhat difficult or the forum get flooded with spam.