How to add a popup for custom fields..

[Mr Pink]

Hi, I need some advice for add a popup menu in the postib(_legacy) for users that have, for example, a certain custom field.

For example..

Custom field: Your Nation.

User called Mr White put there "New York".
User called Mr Brown put there "New York".


In Mr White's post now the field "Nation:" is showed.
It appear like this: Nation: New York
And when the New York link is clicked, it show a popup whit:

New York:

Mr White
Mr Brown
etc.

(somethink like the buddy list popup)

Is it possible?
If yes, wich is the best way for do something like this?