This module adds the ability to edit a single element. The element needs to be surrounded by a DIV with the right things in it. This can be achieved by using something like contemplates,
You will need something like this:
<div class=ajaxeditable nid=<?php print $node->nid?> field="field_[name of your field]">........</div>
More entertainingly, you can install editablefields, and then all the nice views you build with that will magically be editable using ajax....
Since editablefields is the only thing to use this, and it become more and more entangled, ajaxeditable has been merged into editablefields as of Drupal 6. - this module is not supported after drupal 5.