On new profiles make them use a captcha for the first 10 posts.The captcha should be constructed like this.10 pictures of famous places around the world. Make the random.Make the poster answer what the picture is and VOILA!Forum spam free
I just installed a check agains http://www.stopforumspam.com maybe this works...
As for the questions, define 10-20 questions and ask for 3 at registration. That will shuffle them and make it so that bots don't store your Q&A easily.