You can definitely do this with the hook_menu() function.  It'd look almost exactly like the tutorials you'll see out there for an AJAX request using hook_menu()

hook_menu() lets you create your own URL that can access any Drupal or custom function, including making something that just spits out the info you want.

Internal URL or menu callback to use node/entity content without html/page wrapping
I am the webmaster for a school that uses Google Apps for Your Domain, so every family has an account at our domain.  We would like to create a blog that can only be read by school families.  Blogger appears not to support this feature.  (We would have to add everyone in the domain individually.)  Is there another free (or cheap) blog service that offers this functionality, including using Google authentication (i.e., not requiring people to create another password)?  
