I recently had a need to display a CAPTCHA on an ASP.Net contact form. After a short search on the internet, I found this article on the The Code Project: http://www.codeproject.com/KB/custom-controls/CaptchaControl.aspx
This Captcha control by Jeff Atwood was easy to plug in and works very well for my needs. I just wanted to let you know that it is out there.
– Zachary Lyons