Nothing shows up

Seems to me that it would only work with cck fields, according to the description of the module...

Hi Andrey,
As assumed by patchak you need to install the CCK module.
I have scrolled within the code before being able to understand what this module is about.
Let's suppose you will create a Joke module by using CCK. We will keep the two standard fields (Title and Body) and add two select list by CCK: Joke Country and Joke Category.
The respective values of these two fields are:
Joke Country: Spain, Senegal, Belgium
Joke Category: Boring, Absurd, Funny

Test first if your Joke module is working fine (e.g you can add/edit the jokes).

Then comes our module:
Go within the left menu: Administer -> Site Configuration -> Ajax Select
In the content types field select the Joke check box
In the CCK fields select only one check box among the two you have, say Joke Category.
Save your configuration and lets go back to our Joke module.
Add a new joke (specify the country and the category of the joke) and submit it: you will notice some interesting fact after posting your joke: The joke country is shown as a non editable text field BUT the joke category is shown as select list.
Not only that: if you modify the category of the joke and load the node again you will notice that the value was updated without any need of the submit button.

That would be all folks!
/Khalil