How do I create a user submission feed?

Making this as simple as possible..

All I want to do is make a user-submitted form that looks like facebook's newsfeed.

"I want to" [texbox for user input] [ (Post button)

Appears right below:

 [I want to ___________________]

I feel that this can't be too complicated.. I'm trying to have simple code that will allow a user to submit text and have the text appear right below the submission area.

How should I approach this with AJAX? What else would I need? As you can tell I'm a novice.

That's a very broad question. You'll probably want a database, though you could get away with flat text files - at least for a bit. You could automatically generate the RSS xml on request with any of a number of different scripting languages from the database or flat file, or you could update the static RSS feed whenever you post. If you only needed the RSS, the RSS itself could be your storage.

Restrict us a bit more! Give us a language, a persistence mechanism, and what else you want to do with the data.