Getting CAPTCHA on external form (slightly OT)

Hi,  I have a form for posting trade opportunities that is getting flooded by Chinese spam - and I mean flooded.  It is from an old script I am trying to get at least partly working with my limited programming knowledge.  The form is at this link: http://network.caltrade.com/postlead.htm (The captcha you see on there now is from Jotform - just an experiment I was trying that didn't work -people can still post without using it).

How can I get a captcha on this form to block this spam?  Is there a way to use the D7 captcha system?  What about third party scripts or services?  Is there any easy way to do this, or is it an complex undertaking.

Thanks

Rob

Hi Caltrade these maybe a couple of useful links for you

http://www.eniksoft.com/webformspamprotection.html

http://www.webdesignbeach.com/beachbar/ajax-fancy-captcha-jquery-plugin

Thanks Kosmic - those look pretty good, was also playing around with recaptcha for a while, but I think this script is to much of a mess to fix - at least for me.  Can any one recommend a good a good php/mysql code generator?  Don't flame me, I know they are evil, but there is some database content I need to get on my site fairly quickly, and I am not a programmer.

Rob