Problem with Spammers

Hi. Here is my forum... http://www.virginiahotlist.com .

This is my problem. I started this site for fun and to kinda direct people on things in Virginia or a place to complain about Virginia. All of a sudden in the past weeks I have been getting tons of new members every day. I do have a catcha on registration, but they are getting by it. I assume because it is a actual person registering. So what i did is I went to the control panel and now moderate every new member. However i am still getting these people joining.

Please help any advise... I was told to take the catcha off and initiate a auto question something like "What color is wood?" with a simple answer Brown. But I do not see any place in the admin control panel user registration options to do that...

Also Does anyone know ways to generate new members and getting them to post things??