Hi guys. I need help in PHP spam protection (captcha)

I don't know PHP absolutely. I have a PHP e-mail form on my website (http://www.toondra.ru/en/contact.htm) and I have problems with spam. Can you help me and add Captcha code to HTML code of that page? I found that (http://captchator.com/test.php.txt) but it's hard for my understanding :)

If you can help me please send me fixed PHP page (http://www.toondra.ru/en/contact.htm)

Thank you!