How do you include images in my RSS feed?

I am currently using the Arthemia Premium WP theme and need to be able to include the post images in my RSS feed. I am using CaRP to include my WP posts in my Zen Cart ecommerce site. I am also building and iPhone app using iSites.us service. I am pretty new at all of the WP and RSS end of things. I had my Zen Cart consultants looking at it and they said my feed is not including the post image.

Can someone point me to an in depth tutorial on this – also on how to assign specific RSS feeds to different categories in my WP blog.

Here are the site in question: http://www.drnewtons.com (Zen Cart installation)
http://www.drnewtonsnaturalsnews.com (WP 2.9)