easy ajax call?

I'm looking into scripting a block of code that has an image map. when you click on an area, it'll fetch all of a custom content type with a certain parameter.

I know the coding, outside of the drupal interface. Is there a method already available that I can have an ajax script call that'll return content based on certain parameters?

I have a strong programming background, but I can comfortably admit, my experience with drupal is still limited. Ideally if it'll return the rendered code, just as if it was being called to be set on a page, that would be ideal. Any help anyone can offer me would be extremely helpful.