observing textfields in a form (AJAX)

I have a problem and I don't know where to begin with (yes, I'm a newbie ;-)):

I have an application that holds a graph (with nodes and edges). In the view the user enters data that is then converted to nodes and edges: Every formfield-value (in the view) represents a node. I want the user to use existens nodes if possible, so I'd like him be able to see suggestions of neighbouring node-names as soon as enters data in a formfield and changes to another one. It should be a little like the suggestions you get when you post an url to del.icio.us.

---view (form)--- http://pastie.textmate.org/51912

---model (method)--- http://pastie.textmate.org/51913

...the model-method mentioned outputs an array of strings like the following: my_node.get_neighbours => ["a_node_name", "another_node_name", "some_node_name"]

Can anyone point me to some example code where something similar is being made or to a useful documentation? Kind of got no clue where to begin.

Thanks a lot!

Saludos Javier